Table cell strokes are different widths

Hi there,

I've set up a table with a specified number of columns and rows. I've set up 2 styles you can see in the attached screen shots: Black Stroke, and Pantone 314C Stroke. Black was a duplicate of Pantone 314C and the only change I made was the colour of bottom stroke. This somehow causes the width of the stroke to creep over the cell boundaries, causing strokes in my table with unequal stroke widths. Can anyone shed any light on this at all? I've attached appropriate screen shots for you, and can supply more if that helps.

Thanks in advance!

Tabrez.