I've also noticed this. For instance my drafts folder says I have 9 items inside it but in reality there is only 1. When I go into the folder it shows 1-1 of 9
I do normally use Thunderbird so I'm not sure if it's related but one of my users pointed out to me that he had nothing in his drafts folder but it still showed 1 message. After creating a new message, saving and then deleting it the count went back to 0.