Stalling at idle in gear

If the lock-up is staying engaged, then it would seemingly "Push" you forward until it stalls due to the brakes locking up the engine. When it unlocks you go back to fluid only which(at lower Rpm's) shouldn't push you very hard and shouldn't stall the engine. I can't see how Stall speed could affect anything at idle. If your "stuck" in lock-up then it's kind of like trying to stop a 4-speed without pushing the clutch in. I guess what I'm getting at is that if it doesn't feel like you're stalling out a 4-speed then I don't think the lock-up is failing.