AH HA! I've duplicated this issue by following ImA4Wheelr's link here at post #221. I was tipped off to the issue because he says in the post that he's linking to post#461, but when I click the link it shows me a post# of 761! If I click any page number and then click the correct page number I am shown the correct post#461! I'm guessing it has to do with the "Posts per Page" setting (mine is on the default of 50 per page - what is your's ImA4Wheelr?).
Here is what I see clicking the link (Hmm . . . looks like Photobucket reduced the quality of my photos, but you can still make out the post#):
Here is what I see when I change pages and come back to the correct page:
So I'm not crazy! Well maybe I am, but at least I think I found the cause of this issue and proved it REALLY IS happening!
Oh, and the post count is not changed by "50" necessarily, but by a factor of 50 (again based on the other user's "post per page" setting).
-Garry