Configure Project: Remember changes when switching to another project

How to reproduce

1. Open a *.pro
2. In the "Configure Project" (Projects mode) widget, edit a build dir path (e.g. build dir for debug mode)
3. Switch to another project
4. Switch back - your changes are gone!

Why it's useful to save the changes
Let's say you remove the "-qt_4_8_3-Debug" suffix of the build dir. Then you would like to place the build dir inside the build dir of another project (e.g. qt creator tests build dir inside the qt creator build dir), so you switch to the other project to copy the build dir path or some relevant part of it.