Strange Text Messaging Problem

Well, my first guess would be that maybe you've got an "unanswered" alert in your phone somewhere.  Check your "missed calls" log, your pic mail, and your email to see. 

Second, are you getting the "2 new" alert from ALL contacts that send you a text or just one?  I would try deleting all of your text messages from the person that is showing two messages from when you get them.

Third, when you say that you can't "slide" to retrieve your message(s), what does it do.  Does the slider actually move up and down or does it stay in the middle and not move at all?

Have you tried cursing at it?  If that doesnt work then i dunno!!

Ive had this same problem, its been annoying.  I will receive a text and the screen will be locked.  There will be a little blue star at the top and right next to it says "While you were out".  Under that are two notifications: one will show the name of the person texting me and the time and date under it with a little speech bubble indicating that it was a text message.  The other notification just shows another time that doesnt match the time the text was received and has a little icon of an envelope, which i think is used to indicate an email even though i have none. and then at the very bottom it tells me how to unlock the phone, which i have to do every time to read a text.  The sliding screen only shows up for phone calls. 

Whenever i select the notification with the envelope icon it either takes me to the home screen, where i see all my favs or it takes me to the corresponding thread where i can view the text normally.  But so far it seems random in its decision between the two, sometimes i get one, sometimes the other.

I cant find anything on the web to solve this problem so let me know if you guys figure anything out. Ive messed with the settings a lot but to no avail.  Thanks for any help you can give me

OK, so I recently went into the Sprint store to have this issue looked at by their techs.
After working on it for an hour and a half, and hard resetting the phone, they told me that the problem is within the network, and giving me a new Instinct (since I have a full warranty) would not solve the problem. They handed the problem over to their network engineers to let them work on it.  This was a week ago, and the problem still persists.

I'll post if I come across anything or if Sprint tells me what's going on.