With the current Jenkins version having jobs parameterized with "List subversion tag" only one (1) of several entries in the tag-directory are displayed when the following condition holds true:
When the repository was filled/added (during moving from an old repository without history) with a lot of directories, all directories/folders of e. g. SVN tag tree have the same revision number and date/time.
In this case - and this is independent if the top level directory is a tag directory - only one entry will be displayed.
One can argue that this is an unusual configuration, but the manual selection of a tag entry during start-up of a job implies that the user knows what he/she does.