Need to figure out what changed between 1.2 and 1.3. As a work around, installing 1.2.3 explicitly (f0adefc). This needs to be updated though to support newer Sphinx versions.
Fixed with ca2e378. Issue was Sphinx started using sys.argv instead of arguments passed to main. Tinkerer invokes Sphinx by passing in constructed argv to sphinx.main, which doesn't work anymore.