The question is what you expect from INVERSVID. It is mainly meant for text and it causes those areas which are usually drawn in background color or left transparent to be drawn in foreground color and vice versa.
So if you set JAM1 | INVERSVID and then draw lines or other figures which don't use the background color, doing nothing is correct behaviour.
For me INVERSVID works correctly on a 32 bit screen (see attachment).