The problem of the file in T61179 is that the same group starts multiple times.
I'm not sure what the standard way of parsing this is.
Also on this page (http://paulbourke.net/dataformats/obj/) it says that g group1 group2 ...
is allowed. So the same face can belong to multiple groups.
Looks like this is currently not handled in the importer, not sure how often this case exists.