Rendering issues after posting text in weechat

With weechat -> tmux -> mosh -> urxvt, after pasting this text in an IRC channel:

Don't dis­play chan­nel op­er­a­tor priv­i­leges. Dis­play­ing these priv­i­leges on your nick with a "+o" at­tracts par­tic­i­pants who are in­ter­est­ed in gain­ing them and us­ing them ac­tive­ly; it also at­tracts the at­ten­tion of par­tic­i­pants who re­act neg­a­tive­ly to au­thor­i­ty. Have your ac­count added to the chan­nel ac­cess list and op your­self only when need­ed.

This is copy-pasted from here: https://freenode.net/changuide

I get messed up rendering - after some channel switching it looks like this:

54 #python-ops    │12:25:16     @flatcap │ already done :-)                                        
55 #python-testing│12:25:54 The-Compiler │ the channel is registered, and freenode prefers people not to walk around as ops all the time and to just get it when needed ;)
56 #qt-labs       │12:26:08       drymer │ why is that?                                                        
57 #qt-pyside     │12:26:23           -- │ Mode #neomutt [-o flatcap] by ChanServ                 
58 #qt-releases   │12:27:02      flatcap │ the place looks friendlier if we're all equals                                         
59 #qtwebengine   │12:27:15 The-Compiler │ (see https://freenode.net/changuide )                                        
60 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play chan­nel op­   een                                                                                                                                                        60 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play chan­nel op­er­     hain                                                                                                                                                   60 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play chan­nel op­e for­a­er                                                                                                                                                      60 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play chan­nel op­er­a­tor priv­                                                                                                                                             60
49 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­                                                                                                                                             60 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­                                                                                                                                 60 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges. Dis­play­                                                                                                                           60
52 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­play­ing these priv­                                                                                                            60
53 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­play­ing   these priv­i­                                                                                                            60 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­play­ing these priv­i­leges on your nick with a "+o" at­                                                                        60
55 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­play­ing   these priv­i­leges   on your nick with a "+o" at­tracts  par­                                                              60 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­play­ing   these priv­i­leges on your nick with a "+o" at­tracts par­tic­                                                         60
57 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­play­ing these priv­i­leges on your nick with a "+o" at­tracts par­tic­i­                                                       60
58 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­play­ing   these priv­i­leges   on your nick with a "+o" at­tracts par­tic­i­pants who are in­                                      60
59 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­play­ing   these priv­i­leges on your nick with a "+o" at­tracts par­tic­i­pants who are in­ter­                                  6
60 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play  chan­nel  op­er­a­tor    priv­i­leges.   Dis­play­ing   these priv­i­leges  nonoyourinickiwith a+"+o"t­at­tracts r­par­tic­i­pants   rwhon­areein­ter­est­     n  t        u    6          61 #qutebrowser   │                      │ also at­tracts  the at­ten­tion   of par­tic­i­pants    who re­act  neg­a­tive­ly    to au­thor­i­ty.    Have your ac­count aaddedttotthecchan­nel c­ac­cess slistdand your­self only
62 #qutebrowser-rg│12:27:56 The-Compiler │ when needed."                                                               
60 #qtwebkit     1│12:28:40 The-Compiler │ hmm, now my weechat rendering is all messed up, interesting­ing these priv­i­leges on your nick with a "+o" at­tracts par­tic­i­pants who are in­ter­est­ed in gain­ing them and us­ing60
64 #qtwebkit      │12:27:56 The-Compiler │ "Don't dis­play chan­nel op­er­a­tor priv­i­leges. Dis­play­ing these priv­i­leges on your nick with a "+o" at­tracts par­tic­i­pants who are in­ter­est­ed in gain­ing them and us­ing them               
65 #spac­tive­ly; it

I made a typescript (170 MB!) where I connected to the server, switched between the #mosh and #neomutt channel (where it happened), and pressed ^L a couple of times.

Start by reviewing the reported mosh → tmux → mosh → urxvt setup and reproduce the corruption using the linked 170 MB typescript, including switching between #mosh and #neomutt and pressing Ctrl-L. Trace the terminal rendering path implicated by the reproduction; done means pasted text and subsequent channel redraws remain correctly rendered.