Custom build steps are not added to the vcproj file when using QMAKE_EXTRA_COMPILERS and a single-configuration build

I have defined a custom tool to run shiboken and am using mkspec win32-msvc2008.
If CONFIG contains "debug_and_release" then the custom build step is correctly included in the resulting vcproj file.
However, if I am building a single-configuration vcproj file, the custom rule is not included in the generated vcproj file.

Note that I have a patch file which fixes this under Qt 4.6.2 and will probably also work for the latest version of Qt. See attached for the patch file.

Here is my custom tool rule:

SHIBOKEN_RULE_FILE = shiboken.rule
shiboken_rule.name = "Shiboken Custom Build Step..."
shiboken_rule.input = SHIBOKEN_RULE_FILE
shiboken_rule.output = mainwindow_wrapper.cpp
shiboken_rule.commands = ...\shiboken
shiboken_rule.commands += "--avoid-protected-hack"
shiboken_rule.commands += "../data/global.h"
shiboken_rule.commands += "--include-paths=../../HybridApp;$$QT_INC"
shiboken_rule.commands += "--typesystem-paths=../data;$$QTTYPESYSTEM"
shiboken_rule.commands += "--output-directory=.."
shiboken_rule.commands += "../data/typesystem.xml"
shiboken_rule.depends = "../data/typesystem.xml"
shiboken_rule.depends += "../data/global.h"
QMAKE_EXTRA_COMPILERS += shiboken_rule