It happened already few times with different files, always with books.ru search. The app hangs up after viewing the found book meta info in Update by Title dialog.
Web Search -> select one of the found books -> View -> Ok
After that I can only close the app via Task Manager. All the database changes from the current session are gone, e.g. I have to add all the imported files again.
Same scenario, but View -> Cancel -> Update (Merge) works well. So basically it is impossible to change the update settings if I don't want it to hang.