mkspec being deleted from kit

1. Go to "Tools" -> "Options..." -> "Build & Run" -> "Kits".
2. Select a kit which contains a Qt version.
3. In "Qt mkspec", type the mkspec used to build this Qt version.
   I used "win32-msvc2013"
4. Click "Apply".
5. Select somethinge else, e.g. the "Manual" tree node.
6. Select the kit again.
   The mkspec was removed from the kit.

A valid mkspec should not be quietly removed from a kit. When you use a different mkspec than the one used to build the Qt version, this seems to work correctly.