New alerts for old SMS messages

This issue is tricky to describe, but I'll do my best. First of all, I have a Tour on Verizon if that is of any importance.

When I am in a text message screen, I occasionally get a notification that I've received another two text messages from another contact. For example, if I am reading a text from Bob, two notifications will pop up at the bottom showing a text message from Dave. The weird part is that they are an old message and they always appear in duplicates. So if Dave said "See you soon" several weeks ago, I'll see two notifications from Dave that say "See you soon." When I go to that person's conversation screen, though, I don't show any new messages. All I see is the actual old message.

Anybody else experiencing anything like this?

I have not seen that with SMS before, Facebook yes - countless times. It sounds to me like Verizon is having an issue. How long has this been going on?