"I've been thinking of changing this to always save the distance value to history instead of keeping the point, because of that kind of unintuitive side effect that you noticed here.

- Michael"

i can see running into another problem this way. if one purposly extruded up to another object then move the curves you will lose your target for extrusion height, even when placement may be more important than distance. may i suggest a checkbox option to let the user decide, or leave it the way it is since it is much easier to extend an extrusion than to shorten one.