Mesh seperates when rotating in blender

[JTitan]

I never had this problem before. In Blender, when I rotate a part of the mesh to line up with a template it seperates when I rotate it. Does anyone know how to make the vertices stay and stretch with the selected part of the mesh? It always has before but for some reason it is not now .

 

[JTitan]

It seems that when your in face select mode the selected mesh seperates when rotating. Can be solved by using the vertex select mode.