Qt not working on OS X Snow Leopard when built with the 10.7 SDK

Qt always crashes on Snow Leopard with this backtrace:

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_PROTECTION_FAILURE at address: 0x00000000
0x00000000 in ?? ()
(gdb) backtrace
#0 0x00000000 in ?? ()
#1 0x001d8b7b in CopyCTThemeFont (themeID=5) at qt_mac.cpp:52
#2 0x001d863c in qfontForThemeFont (themeID=5) at qt_mac.cpp:68
#3 0x00057010 in qt_mac_update_os_settings () at qapplication_mac.mm:526
#4 0x00059045 in qt_init (priv=0x170ddb0, unnamed_arg=1) at qapplication_mac.mm:1214
#5 0x00136431 in QApplicationPrivate::construct (this=0x170ddb0) at qapplication.cpp:839
#6 0x00137038 in QApplication::QApplication (this=0xbffff990, argc=@0xbffff9d0, argv=0xbffffa34, _internal=17041410) at qapplication.cpp:738
#7 0x0000395a in main ()

This is using the "mainwindows" example, but it could be any Qt app.

This problem goes away when adding "-sdk /Developer/SDKs/MacOSX10.6.sdk" to the configure script.