I must assume this is caused by the order in which these tags are parsed, due to the order of extension installation, which adds BBCode tags to $tags[].

A similar conflict has already been noted elsewhere, which is that pre-parsing posts for URLs can break new tags like [video ].  Turning the URL parsing feature off is no solution, since it omits a valuable function, and the solution must be dug out of the forum.

Both defects point to the need for prioritization of BBCode patterns.  One solution could be an administrator's form in which tag priority can be modified.

Free URLs shouldn't be wrapped in [url ] as a pre-parse action, but rather as a post-parse action.