On mine, the slip light is on only while the system is actually doing something - for that second or 2 I'm on the patch of ice or whatever.
It turns off the second the tires stop slipping.
Just like the way you descibe on your wife's volvo.

If the light stays on after slippage, and is still on when you are on dry pavement, sounds like something might be wrong.

I'd definalely ask the dealer to check this if the slip light stays on AFTER the system is done working it's magic (or voodoo!)

VDC light is not suppose to come one when the VDC system activates - it just shares that same slip light. If VDC lignt comes on and stays on, that aslo indicates something might be wrong.

I'd ask the dealer to check this out....