Thanks for the answer. I'm not convinced of the usefulness of this function. I almost always have Free Snap on, and usually don't have any problems with accidentally free snapping to an undefined point, you can see whether you snap to an actual point by the cursor behaviour. Maybe if you are working very quickly...In the end it's more a pain for me to always have to reactivate freesnap. And the issue as I have experienced it doesn't have to to with dimensions, it happened when just drawing a line (testing that negative prefix bug). In the end of the discussion on #745 it says: "r_a_v_a_s removed this from the 2.2.0 milestone". Maybe a leftover from an unclean removal?
But I can live with it. Just can't use the spacebar to activate command line input, have to click into it.