GDB protocol error when interrupting reverse execution with rr 5.2 and gdb 8.1

Occasionally, if I attempt to interrupt a reverse execution using Ctrl-C in GDB, rr seems to send a reply that is unrecognized by GDB. If I wait and allow the reverse execution to finish, I can regain control.

(rr) reverse-finish
Run till exit from #0  0x000055d40cbe9046 in stm_wbctl_add_to_ws (mask=18446744073709551615, value=94370124894352, addr=0x55d43962f488, tx=0x14afac000900) at src/stm_wbctl.h:808
warning: Invalid remote reply: 9090c541
stm_wbctl_write (mask=18446744073709551615, value=94370124894352, addr=0x55d43962f488, tx=0x14afac000900) at src/stm_wbctl.h:860
(rr)

With set debug remote 1, I see the following:

remote_pass_ctrlc called
remote_interrupt called
Sending packet: $bs#d5...Packet received: 9090c541
warning: Invalid remote reply: 9090c541

I'm not sure if this is a bug in gdb or rr, as a quick skim of the documentation for this portion of the GDB stub protocol suggests that GDB can send either 0x03, vCont, or vCtrlC, depending on the mode of execution. Since I don't see any mention of QNonStop+ in rr's qSupported response, execution seems to be in all-stop mode, which would suggest GDB should be sending 0x03.

No source file or test is named. Reproduce with rr 5.2 and GDB 8.1 by interrupting reverse-finish with Ctrl-C, then inspect the set debug remote 1 trace and the qSupported response against the GDB interrupt protocol. Done means Ctrl-C produces a reply GDB recognizes instead of 9090c541.