The common factor in all these crashing reports appears to be the use of a text field with completion. For example, editing authors in the main books list or editing authors in the edit metadata dialog. That helps me narrow down the possibilities. I still cannot reproduce the problem, but I can try a few things, stay tuned. It would be very helpful if one you can setup calibre to run from source on your computer, that way I dont have to create a new build every time I want you to test something. Instructions for doing so are here:
http://manual.calibre-ebook.com/develop.html