I have the same issues with the modify menu bar in 8.1...
it has something to do with using the "continue action" arrow on the bottom of the left hand toolbar, using that arrow after I select the item continues the action of scale, mirror, etc....so it works in 8.1 but definitely has a flaw in it compared to how it works in linux, version 2.02
Neal
PCLOS-LibreCad 2.02
Windows, 7 & 8.1, Librecad, 2.06