Hello ! Indeed - I figured it out and appended my previous post ... probably just as you were typing your reply :D

All that said, since the behavior of selecting "polylines" in the export dialog is indeed dependent of the state of UseSimpleEntities, then I would say that this does require for the flag to be switchable in the export options indeed as briefly mentioned above - especially since one would assume intuitively that a "circle segment/arc" is a subset of the group "curve" ... even though in the DXF sense they are distinct separate entities.