Actually, I now don’t think the 0 was a bug. Instead, the bug was having space AFTER the arrows. The rule is generated based on the value of the “Add space between desktop menu bar items.” option. So that should mean what it says – and include the arrows.
It is also a possibility that there is a problem with no value and 0, and 0 should be considered by logic to be the same as no setting. I think the intent of that admittedly obscure option id to control that particular spacing.
So I’m thinking the real problem is that 0 doesn’t make sense for that option at all, and that maybe the generated CSS still doesn’t handle it all correctly for arrows vs. none.