Initial thoughts:

*   Widget is not disabled when a database is not open
*   When 'Browse Data' tab is clicked on, X axis gets unticked (ie, when user flips from execute SQL to Browse Data) Two 'rowid' rows momentarily exist in the grid, but this is just a quirk of the grid re-populating I think.
*   When an item in the X axis is ticked, ticking another item unticks the original item, but the item you clicked on is not ticked, so you have to click the item you want again.
*   When selecting 'row #' as the X axis, '65536' is displayed as a label, rather than 'row #'.