Trash is empty but shows number

I've had this problem a # of times. I've discovered that the source of the problem is this; when I open my trash folder to begin emptying it, there is a lag where at the bottom of the screen it says "connecting". Your trash folder is being updated how many messages in trash have been unread. If you start deleting messages before your folder is updated and one of the messages you deleted is unread, it will leave a number of unread messges. So if you deleted one unread message prior to the folder catching up, at the end of your cleanup you will see Trash (1) at the top. If you are quick enough to delete two messages before the folder catches up you would see Trash (2). Then if you were to the following day do the same thing, the number will increase. When cleaning up your trash folder, it is important to open the folder and give it a few seconds before deleting any messages.

If you already have this #, the only way I've found to deal with it so far is to go to your Settings > Mail Settings and delete the account and then set it up again. This should clear that number.