Well 0.7.26 had no changes that would affect your issue, so I'm not surprised it didn't help
As for fixing the problem you will have to use the command line tools to do that:
Run
calibredb list > output.txt
Then run
notepad.exe output.txt
That will give you a list of books with id numbers in the left most column. Fin the id number of your problem book and then run
calibredb remove id_number
where id_number should be the number you found