Is this a bug? Or a feature?

It took me a while to figure out what was going on here, so I made this example to show it:

If you make a Brep from an extruded multi-part curve and then trim one end with another Brep, the endpoints of the trimmed edge move to a different place. This causes very strange results if you then use this edge curve with one from the original, untrimmed Brep to make a Loft or Ruled surface.

Is this a bug?  Expected behavior? Or am i just missing something? What I did to get around this was to trim a tiny bit off the original BRep too - so it's top edge endpoints would end up in the same relative place as the trimmed one.