I still can’t track down the ARD bug. I found an alternative that works: 1. Log in via ARD and see the garbled screen 2. Log in via SSH in the Terminal, and restart ARD using “sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Conte
nts/Resources/kickstart -agent -restart” 3. Voila! It’s fixed!

I’ll still hunt for the bug until Apple releases a fix.