For the EOS-1V - and other similar cameras, MLU has to be a deliberate effort as you have to be aware of the dangers when using it. In the manual it states the following.
• In very bright light such as at the beach or ski ground on a sunny day, take the picture promptly after mirror lockup.
• During mirror lockup, do not point the camera lens at the sun. The sun’s heat can scorch and damage the shutter curtains.