Hmmmm. I don't have 4.2 yet and wasn't concerned about forward compatibility until your post Above..
Usually, an Older Java SDK is good moving forward. I would have been more concerend with New Stuff Created with 4.2 working completely in a 4.1 environment.
I will research incompatibilties. Can You give an Example or Two were the New Broke the Old.
Criticism accepted for Solutions that work. ;^)
Sabayon 11-DEBIAN 7-#Sid-Slackware 14-Calculate 13-