I think this is why that happened:
- "MOVED: " topics don't normally increase your post count. (I think.)
- I recounted all post counts recently, and this included "MOVED: " topics.
- Later, I deleted all "MOVED: " topics and recounted again.
<…> There are a few rare mod/admin actions which change your real number of posts but neglect to update your post count.
- Errors can occur which can cause it to drift from the real value.<…>
<…> There are several bugs which cause the post count to drift from its real value over time. <…>
I figure there are still some circumstances (i.e. moving threads) that cause the post count on the profile to differ from the real number of posts (excluding zones where they are not counted, such as Serious Discussion & Ivory Tower).