I think its a bug.
I get that sometimes when I get a text and I read it but the 1 is still there.
Also after reading a new sms, the icon on the notification bar stays there too but thats easy to remove as u just press clear.

Also noticed sometimes I cant add anything to my homescreens. I press and hold and it comes up with the usual menu for widget, program etc but when I select something nothing happens.

 

Yup, I get the same. The way to reset the count is to delete *any* message. That seems to clear the bug.

 

Another way round it is to remove the widget by long holding and dragging it down to the remove part of the screen and then adding the widget again in the normal way - the green "1" will then have disappeared

 

I've noticed this, but it disappears fairly quickly. It's more of a delay than a problem in my case.

 

I've noticed this, if you send a text and receive another before closing down the messaging app it happens.

upon receiving another text seems to rectify the problem though, its just a little annoying