Adjacent table cells with different border strokes.
I'm attempting to create a Punnett's Square using tables. A 2x2 grid with labels along two edges, like this:

My plan was to create a 3x3 table with two cell styles. The outer cells for the labels would use a style with no border; while the inner 2x2 grid would use a style with a border on all sides.

For some reason, however, the resulting table looks like this:

It seems to me that the cells without any border have a higher priority than the cells with one. Does anyone know how this priority is determined, and if it can be changed?
