Switching from non shadow to shadow build still tries to use ui_xx from non shadow folder

Strangely if ui file is changed and then build folder is switched to shadow. Makefile still refers to old location for ui_xx files.
Steps to reproduce:
Start a new project in Qt creator with simple gui.
choose build folder as source (not shadow)
Build and run
Change Ui file (add another label)
Switch to shadow build.
Build and run to see it is still showing old ui.