Member power level picker traps users in integer-mode if they pick 'Custom level'

A user reported clicking 'Custom level' to see what it did, only to find themselves faced with an integer value field that they then couldn't escape (they tried entering random numbers but couldn't figure out how to get back to where they were).

In my testing I noticed that, if you just leave it alone for a few seconds on a value that == a set value (i.e. 0 for default, 50 for mod, 100 for admin) then it magically goes back to displaying that text (even if you maintain focus on the field, which is pretty surprising).