UnityYAMLMerge tool does not work with external tools that take switchs with slashes on windows 10 creators fall update

I'm trying to get WinMerge to work with UnityYAMLMerge by adding the following line to mergespecfile.txt
* use "%programs%\WinMerge\WinMergeU.exe" /e "%r" "%l" "%d"

However when WinMerge is launched the command line looks like this in Process Explorer
C:\Program Files (x86)\WinMerge\WinMergeU.exe" \e "C:\Users\dkhje1\AppData\Local\Temp\MER79A.tmp" "C:\Users\dkhje1\AppData\Local\Temp\MER798.tmp" "C:\Users\dkhje1\AppData\Local\Temp\MER856.tmp

Which seems right but WinMerge will complain that the left file path is wrong and print it as "D:/e"

Same thing happens if I try unsing the predefined Araxis Merge which also uses slash switches except it will complain that both left and right files are wrong and show "D:/3" "D:/a2"

I produced the error trying to merge the two conflicting commits in the provided Mercurial repository using tortoiseHG

FIX
Update the mergespecfile.txt entry for WinMerge to the following:
* use "%programs%\WinMerge\WinMergeU.exe" -e "%r" "%l" "%d"