Silverlight 4.0 DataGrid Issue

I have changed DataGrid's DataGridRowGroupHeader's controltemplated and have pl开发者_如何转开发aced 1 checkbox and 1 textblock instead of content presenter. now when i do grouping... in some cases if i click on checkbox of one group... it automatically selects another group also. can anybody please give some advice for this?

I had ScrollbarVisibility= true for Datagrid... and when i was scrolling the grid... checkbox selection was changing... i made scrollbarvisibility to false for datagrid and placed the datagrid in one scrollviewer and it worked fine... i am surprised from this behaviour of datagrid's scrollbars.