I am using the grid is listbox single selection mode, and therefore could not take advantage of the built-in dragging/dropping of columns for column arrangement.
I added my own mousedown/mouseup handlers and it is working as I would like. I noticed that when I dragged a column to the far left (to column index 0), I got a null reference exception.
I removed all of the grid event handlers and was still able to replicate this behavior. However, in a separate test project I cannot mimic this behavior.
Ideas? The stack unwind is attached.
This may be related to an 220.127.116.11 issue that we have fixed in out code base here. We will have a 2.1.0.x release any day now, but if you want to try a private build before our public release, you can submit a Direct Trac support incident and get download instructions there.