Marvin,
Your post explains a great deal about the difficulty I have been having using the "invulnerability" option and seeing it granted in turn to my foes!
Now if I could just figure out why the C&C3 game crashes 9 out of 10 times I hit a funtion/option key then I would be set.
PS
I would have that problem when applying multiple options one after the other.
Ex. F1/F2/F3/F4 ...
Problem was resolved when I waited a few seconds between the different option activations
Ex. F1 ...F2 ...F3 ...F4
Hope it helps