Just a heads up.
I just had Count Pages crash Calibre upon updating a previous count.
8.7 on XP SP3
Repeated 3 times.
counted pages on a title, clicked OK to update . Crash.
Started Calibre Noted it did change the first time.
Tried again: Crash
I tried another title and it worked,
Tried title 1 and it crashed
Opened title1 Metadata editor and saved.
counted again: Joy