Qt Creator + Qt 4.7.3 on Mac OS 10.6 - always builds x86_64, but I only want 32 bit

When I compile my app that uses some 3rd party libraries built for x86 and PPC in Qt Creator, I get "missing required architecture x86_64 in file...." errors. So obviously it is compiling for 64 bits - which I don't need. The compile output window indicates "-arch x86_64 -Xarch_x86_64".

In my .pro file I have:
Qt Code:
CONFIG -=x86_64
CONFIG +=x86 ppc

Which I understand will tell the compiler to not build for 64 bits.

Here is some output from the compile window, which seems to prove the compiler is being directed to make a 64 bit version:

g++ -c -pipe -O2 -arch x86_64 -Xarch_x86_64 -mmacosx-version-min=10.5 -arch ppc -arch i386 -Wall -W -isysroot /Developer/SDKs/MacOSX10.5.sdk -DNDEBUG -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB -I../../../QtSDK/Desktop/Qt/473/gcc/mkspecs/macx-g++ -I../

I see there are multiple -arch parameters there. So where are the "-arch x86_64 -Xarch_x86_64" coming from?

I've also tried with just:
CONFIG +=x86 ppc

When I look at the "Build Settings" for my project I notice:
"Qt version" is "Desktop Qt 4.7.3 for GCC (Qt SDK)" and is grayed out.
"Tool chain" is "GCC (x86 64bit)" and also grayed out.

The Qt version tool tip shows:
ABI: x86-macos-generic-mach_o-32bit
ABI: ppc-macos-generic-mach_o-32bit

On the Tool Chains panel it shows:
Auto-Detected Auto-Detected
GCC (x86 64bit) GCC
GCC (x86 32bit) GCC
GCC (ppc 64bit) GCC
GCC (ppc 32bit) GCC
Manual Manual

This issue also happens with the sample apps, so it isn't something unique to my .pro file.

I have Xcode 3.2.6 installed and it will compile my app OK as 32 bit only when creating an XCode project from the .pro file.

See forum post here:
http://developer.qt.nokia.com/forums/viewthread/9156/