Qmake system test function always returns success in Qt Creator

The "system" test function always returns success when I run qmake through Qt Creator. The same issue does not exist when I run qmake from a terminal.

The easiest way to demonstrate is to put this in a qmake file. It should always print the message "false".

system(exit /b 1) {
  message("true")
}
else {
  message("false")
}

If I run qmake from a terminal I get the expected "Project MESSAGE: false".

If I run qmake in Qt Creator I get "Project MESSAGE: true".