Sorry for the barrage of emails, further details:
I have tried with the latest git master branch (GNU Emacs 25.0.50.1 - commit c477f207) and I so far it hasn't crashed. However, what happens is strange keyboard behaviours after I have done similar steps to cause a crash in 24.4.
Now on single keypresses I get several characters I do not expect along with every keypress. These extra characters will also show up if i start typing in the main buffer also.
When helm is searching, things can get a bit slow, and I think many of the keypress events are getting bundled up somehow and not released? So every keypress from then on in is getting ALL of the events. It is easy to make the number of characters grow by just typing really quickly when it has gotten slow.