Roof operation quirk ???

I have something strange going on with the roof

If I hold the button to close the roof, and keep it held after closing and the "bong" is heard, and the "roof closed" text displayed, all 4 windows will then close ( they're supposed to ),
but then sometimes - not every time - the drivers window will open again and stop about a third of the way down

Has anyone else had this happen, or have any ideas why it would do this ( sometimes ). I thought it might be due to the window sticking, but it only ever does this after the roof closing procedure, the window has never re-opened after closing it in normal use. ( Or is it just me ? )

Been to the dealer once with it an it was a "No fault found" report from them,
although they haven't ( yet ) witnessed this happening.