The WiXInstaller project fails to build producing this error: 8>light.exe : error LGHT0001: Item has already been added. Key in dictionary: 'reg4C319E0ED180C06D6119D1C7C06F39B7' Key being added: 'reg4C319E0ED180C06D6119D1C7C06F39B7'
I traced it down to duplicate w:ProgId tags getting generated in the .wxs file. This seems to have broken with commit 4ece0f178908b754d178 and the change to FixFragment.xslt.
On Windows, with WiX installed, create an empty default project and compile it. No additional code is needed to see the error.