eslint: v3.6 ignores "smart-tabs" rule and notifies of indent errors

I’m a maintainer of Leaflet, and we use an eslint config with smart-tabs, like:

      "no-mixed-spaces-and-tabs": [2, "smart-tabs"],
      "indent": ["error", "tab", {"VariableDeclarator": 0}],

eslint 3.0 through 3.5 work just fine. However, after an upgrade to eslint 3.6, we’ve got error messages like the following:

/home/ivan/devel/Leaflet/src/control/Control.js
   64:7  error  Expected indentation of 2 tabs but found 4 spaces and 2 tabs  indent

This can be reproduced by checking out the Leaflet repo, then running npm install and then npm test. Note that running npm install eslint@3.5 then npm test will work as expected.

We don’t use any transpiler in the Leaflet toolchain; full eslint config is available on the Leaflet repo; and the bug is reproducible on the environments of more than one developer.

Looking at eslint’s changelog, I’ll guess that this is caused by #7076 (ping @not-an-aardvark)