Multiple instances of OS X in one Mac: Mac App Store issue

If you need a second instance of all your developing environment on the same Mac, you will encounter an annoying issue with the Mac App Store.

It seems that the store sees the apps you installed on the "old" partition and doesn't allow you to install again your apps on the new environment.
How to fix that? You can't. But there is a workaround that works

unmount temporarily the other partition before using the Mac App Store

Bug fixed. Let's move on...

(source: http://apple.stackexchange.com/questions/32069/mac-app-store-and-multiple-os-partitions)