All my flags that were raised before April 2011 are marked as "active", except spam/offensive flags which are marked helpful:
Checking some, they were obviously helpful (e.g. post deleted as result) so most likely the "helpful" bit was not recorded yet back then.
I don't think it should stay "pending" forever, better just remove it and put "status not recorded" or something like that.
Worth also to mention, this is causing a mis-calculation in the new flag history, as reported here: My flagged posts count is missing one