Why are picture texts going into a separate group text?

A

AC Question

When a friend sends me a picture, the stock messages app creates a group text (containing just my friend and I) for the pictures, yet the thread we were texting in is still there. Why does it create a 2nd thread just for pictures and how can I stop that from happening? I just got the note 4 yesterday and was previously using the note 3 and never had this issue in the stock messages app. Thanks