Starting maybe 2 weeks ago, if I have multiple new Gmail messages, when I go through and delete them via the notification bar, when I get to the last new notification, it will automatically act as if I swiped it away.
For example, say I have 3 new emails, and notifications for all 3 in my notification bar. I expand the first notification, click delete, it's gone. I expand the 2nd notification, click delete, it's gone. As soon as the 2nd notification disappears, though, the 3rd notification also disappears. The email remains in the inbox but I have to switch over to the Gmail app in order to delete or reply to it.