MacBook Pro connected to Dell monitor display issue
Given that nobody seems to have any idea what the solution might be, I'll give you the Ask Different Backup Answer to Hardware Problems (aka ADBAtHP): go to your local Apple Store (or Apple Authorized Reseller) and ask them. Take your Mac, the adapter, and the monitor so they can reproduce it. They'll probably try other monitors, other adapters, and other Macs to see what the issue might be. Hopefully you're under warranty and/or it's just a bad mini DisplayPort adapter, as that's the cheapest fix.