By default win32-msvc2010/qmake.conf has QMAKE_CFLAGS_DEBUG set to "-Zi -MDd" and Qt compiles ok and vcxproj files generated are ok. However, if you set it to "-Zi -Mdd -Od" (disable optimization) the resulting vcxproj file leads to an incorrect vcxproj file as the optimization level remains O2.

The fix is in msbuild_objectmodel.cpp: the static function "toString(optimizeOption option)" needs to return "Disabled" if option is "optimizeDisabled":

static inline QString toString(optimizeOption option)
{
    switch (option) {
    case optimizeMinSpace:
        return "MinSpace";
    case optimizeMaxSpeed:
        return "MaxSpeed";
    case optimizeDisabled:    // fixes problem where -Od is ignored
        return "Disabled";
    }
    return QString();
}