OK, this has been buggy for a long while and it's code I wrote, so you have my apologies for being a sloppy programmer and taking so long to fix it!
However I finally sat down and think I've fixed it so that the count goes up and down as it should. However if your count is already wrong the indicator will continue to flash even when you have no new messages. If this is the case then what should happen when you the
Received PM page the counter should correct itself.
If anyone continues to have the indicator flash when they have no new messages and
have visited the Received PM page then please let me know.