notification still in notification center after mail is read

Step to reproduce:
1. get a new incoming mail, a notification shows up; OR [having several incoming emails, unread]
2. read the message in mailmate, without clicking the notification (since the notification can auto hide after some timeand one only noticed new mail from the dock icon) OR [clicking one of the notifications in the case of having several incoming emails]
3. read all unread mail
4. now there are no unread mail; but notification still shows in notification center

Expected: when reading an unread mail, the corresponding notification should be cleared when the mail is read.

Thanks!