My client was just having this issue, but only on his account (well, no one else reported it to him, so there may have been more)
I optimized the database table, used the recount tool and that didn’t fix it, but if I accessed the topic directly from his account and made a post, the link would then be fixed. Then I hit “Mark All Topics as Read” and those certain post links would mess up again. I deactivated the Unread Posts (0.9.3) plugin and the bad links were immediately fixed.
My client was just having this issue, but only on his account (well, no one else reported it to him, so there may have been more)
I optimized the database table, used the recount tool and that didn’t fix it, but if I accessed the topic directly from his account and made a post, the link would then be fixed. Then I hit “Mark All Topics as Read” and those certain post links would mess up again. I deactivated the Unread Posts (0.9.3) plugin and the bad links were immediately fixed.