In the file below, the red inner arc is an offset from a sub-object selected outer (upper) blue arc segment of a closed curve.
Now, try trimming away the upper blue arc part using the red offset curve as the cutter. The trim works, but when you complete the command, the red arc also disappears - because its history-parent has been trimmed away. Leaves one small line segment on the left side as well, which is odd.
HistoryTrimQuirk.3dm (2.5 MB)
I think in this case history should be broken and the red arc preserved?