Choosing multiple rows/cols in different ways yields different selections

If you select columns by first selecting say column 0, holding the mouse button down, dragging to column 5, the selection registers as a column selection.

If you select columns by first clicking on column 0, hold shift, then clicking on column 5, the selection registers as a box of (0,0,0) to (<#Rows>,5,0).

This affects the OnRowSize and OnColSize implementation in #66.  I'm not really sure how to track down how this is happening.