So that explains the keycoding, I found a MM5740 datasheet and one of the tables has:

CTRL+SHIFT+P makes NUL,
CTRL+SHIFT+M makes GS,
CTRL+SHIFT+N makes RS

I don't know why they duplicated lines in the datasheet, though for M and N where it doesn't have the different SHIFT+CTRL.

[Linked Image from i.imgur.com]

duplicate lines for P

[Linked Image from i.imgur.com]