OK, I got you. Nothing suspicious and apparently no "electronics" in between the 2 devices. As I have little experience with ALGE, is there a software tool available that shows what the driving software actually sends out? My bets are actually on the display side to be the problem. I would try with another PC (I know, RS232 interfaces are hard to find these days) if it has the same effect on the display.
Cheers
M.