Ok, thanks to both. In the meanwhile, mjl pointed me to
http://www.ietf.org/rfc/rfc3986.txt, sect. 7.3, where this can found:
"Note, however, that the "%00" percent-encoding
(NUL) may require special handling and should be rejected if the
application is not expecting to receive raw data within a component."

This apparently could be the reason behind the current behaviour of webfs.

I'll try and fix that in webfs unless somebody beats me to it (please
do! ;) ).

Cheers,
Mathieu