The area operations 'Intersect Areas', 'Cut away from area', 'Area XOr' should reject line objects.
See the attached map example. Selecting the two areas and the lines crossing them leads to undesired resuls. Also applying these tools on the two line objects on the left side shows that these operations are not useful.
I can't see any use case in the moment, where applying these tools on line objects makes sense.
Maybe it makes sense to take the selection of objects and deselect all line objects before applying the area tools on the remaining objects (none of course, if only line objects were selected).
I don't think I will make these tools more restrictive.
At least I can imagine cutting dark green at a bordering road.
I agree that this might be a use case for the cut away operation.
So, please close this ticket.