Installation of commercial OS X 4.6 debug libraries does not work

I'm used with the following procedure for a long time:
1) install the Qt binaries
2) install the Qt debug libs

From the 4.6 release, the installer (step 2) erases the old debug libraries, but not copy new ones. Yet, the installers finishes with "success".
I could verify this under 2 different machines (10.6 and 10.5).
The current work around, is to unpack oneself the debug package and copy the debug libraries one by one in their proper Framework locations.