Currently, if you remove the ground a builder or platformer is standing on, he still continues his skill. I cannot see any justification for changing the digger behaviour unless these platformer / builder behaviours are changed too.
Many other skills exhibit similar behaviours as well. For example, bashers and miners only check for "am I still standing on something" on certain frames (the ones where they move).
I can see valid arguments for changing this in all cases, but I do feel it's a very radical change that definitely has the potential to break entire levels, not just break a replay or two, so I think keeping the current behaviour is preferable here.