bug#38802: 24.5; emacs unusable, unpredictably, with "k is undefined" for every key

[Samuel Wales]

i will try to post a screenshot next time.  it could be quite a long time.

i think i forgot to mention that the password prompt, in the most
recent instance, was triggered by shell mode.

any suggestions of what to put in for a sigusr1 or sigusr2  would be
interesting.  i could put debug there maybe.  or find out what modes
are active, or the values of hooks.