When attempting to use a URI with a protocol that the parser doesn't recognize ('svn', e.g.), instead of creating a link (I didn't expect it to), or displaying the text as is (preferable), it seems that, beginning with the double-slash, it goes into "unparsed block" mode until it encounters another double-slash. IIRC, this duplicates the double-percent tag.
I've tested with all plugins disabled (other than those that the plugin form won't let me, obviously).
I also tested it on the dokuwiki.org playground, and reproduced it there.
Example, to reproduce:
* This is a subversion URI
* This section should appear as a nested unordered list, but doesn't
* This is a mythtv URI
* This nested OL should appear properly, but the URI is hosed.