PredefinedMappingBox: fix regression by ada40e4ce1d9f8e064a0428287c66c0774ecebcf :
If the user chooses a saved mapping, then chooses CUSTOM for editing it and then changes it back to its original settings (e.g. disable and re-enable one item), the selection goes back to the saved mapping. This makes the custom mapping panel disappear!
Merge pull request #79 from mgmax/develop

PredefinedMappingBox: fix regression by ada40e4