This isn't quite the bug I thought it was going to be. I couldn't reproduce it. Though it occurred to me that the other logical explanation is that you do have 9 pages of watched threads but the only threads on that page are actually be users who you ignore.
Could that be possible? If you view the page source you'll likely find some thread list items hidden with CSS.
I just reproduced it myself, so there is a bug here - there isn't the usual link to unhide ignored content - but would be good to make sure I'm fixing the right thing