lucy24 - 11:12 am on Sep 30, 2012 (gmt 0)
Curiously, the border-collapse version works if I change the cell border style to "dotted". In that case the black border magically appears.
Not curious at all; it's part of the border specification. See Border Conflict Resolution [w3.org].
Short version: when there are conflicting borders, might makes right and bigger is better-- except that "hidden" trumps everything.
narrow borders are discarded in favor of wider ones. If several have the same 'border-width' then styles are preferred in this order: 'double', 'solid', 'dashed', 'dotted', 'ridge', 'outset', 'groove', and the lowest: 'inset'
So if you could bring yourself to make the table border just one teeny little pixel fatter, your problem would be solved. Or try setting the overall border to "double". This obviously has no meaning when it's only 1px wide, but give it a try.