(Edit after the fact by @nex3)

Tasks:

• Deprecate existing behavior in stable.
• Remove behavior from master.

I know the existing behavior was intentional, but it breaks the basic rules of math: if 1px == 1 and 1 == 1em, then 1px == 1em. That sounds like a bug to me. In CSS the actual unit or lack of unit is very important. I can't think of any real use-case where I would be equally happy with or without a unit.