Unable to load plugins between sessions with universal binary on Mac

This is separated from http://bugreports.qt.nokia.com/browse/QTBUG-1736 as suggested.

The current plugin cache implementation prevents users from using plugins compiled as universal binaries on Mac. We have a 32-bit Carbon/64-bit Cocoa application and custom Qt build.
So, after application is launched in 64-bit mode, it is impossible to successfully load same plugin in the next session if application is started in 32-bit mode.
This is huge issue for us and it affects pretty commonly used plugins - image loading (gif, jpeg, tiff, etc.).