The trainer keeps a buffer of other typed keys. So, if you pressed "S" at any time before pressing F6, it would also record this keystroke and enable this function. This is most likely what is causing the result you're seeing.
As far as as "everyone" getting a cheat, not unless you're selecting or mousing over other units before deactivating the cheat by pressing V or F6 again. The trainer doesn't know you from the enemy, all it knows is what is being selected or moused over. If you mouse over the enemy or have the enemy selected or all your troops once you turn the option on, then it will be applied to them.
[Edited by PWizard, 4/18/2007 6:45:32 PM]
I was pressing X instead of V
Everything works like a charm with V
Thanks