Welcome to the forums, Acacia.
I can only guess that the forums' verification will remain until a certain post count, or until you have been a member for a certain amount of time.
However, I never had to verify when I had posted (only when I had registered here). So it is hard to say which...
None of us (including you) had this problem yet Acacia had to deal with this problem? Hmm, the system is clearly rigged.