As written by Martin Kletzander <mkletzan@redhat.com>:
Since commit 8eb55d78, when you parse
and save an URI that has no server (or similar) part, two slashes
after the 'schema:' get lost.  It means 'uri:///noserver' is turned
into 'uri:/noserver'.

basically
   foo:///only/path

means a host of "" while

   foo:/only/path

means no host at all

  So the best fix IMHO is to fix the URI parser to record the first
case and an empty host string and the second case as a NULL host string

 I would not revert the initial patch, we should not 'invent' those
slash, but we should instead when parsing keep the information that
it's a host based path and that foo:/// means the presence of a host
but an empty one.

Once applied the resulting patch below, all cases seems to be saved
properly:

thinkpad:~/XML -> ./testURI uri:/noserver
uri:/noserver
thinkpad:~/XML -> ./testURI uri:///noserver
uri:///noserver
thinkpad:~/XML -> ./testURI uri://server/foo
...