This issue is not a bug but it's more a design problem. Because Subversion
doesn't force to respect trunk, branches and tags convention, P.Mézard chose to
design svn convert tools to be able to deal with any situations (where an svn
repo doesn't follow the svn convention). But to do this, we should scan svn
history to discover the relations between the mainstream branch and tags and
this takes a lot of time if there are a lot of tags like in Lyx svn repo.
Added to this, there are special cases like tags renaming which we should take
care and it implies to scan svn history which is expensive operation in big repo.
Added to this, there are special cases like tags renaming to take care of this
we should scan svn history which is expensive operation.