Creation of an encrypted file system works. Writing to the filesystem works also. Unmounting it works (using fusermount -u) Later re-mounting it (using encfs) results in an error:

encfs: ./boost/spirit/utility/impl/chset/range_run.ipp:123: void boost::spirit::utility::impl::range_run<CharT>::set(const boost::spirit::utility::impl::range<CharT>&) [with CharT = char]: Assertion `r.is_valid()' failed.

I tried many options, syntax variations, FUSE options and so on to no avail.
This error is easily reproducable.