Hi nameless, so there's a thing built in to Sweep called "autoplace mode" which determines whether the sweep should start directly from the curve as given, or whether the profile should be moved and rotated to the start of the path curve and then swept starting from there.

Autoplace mode is implicitly turned on or off depending on whether the profile curve is inside the bounding box around the rail or outside of the rail's bounding box.

So your weird result is happening because autoplace mode is off somehow during the history update. That seems like a bug so I'll investigate why it is off then. Other kinds of edits like move/rotate/scale of the whole profile curve seem to be working ok, it's during a control point edit that it looks like there is an autoplace bug.

- Michael