Doors unlock when hitting bumps

[Darrell Woods]

I have a 98 SL500 and the doors will unlock when I hit a fairly hard bump (like a really bad expansion joint). Doesn't happen on normal bumps, but only on the ones that you think "wish I'd missed that one". Once they're unlocked, they won't relock until you turn the ignition completely off, remove the key, put the key back in and turn until the dash lights come on...at that point they are back to working normally. Any ideas?