SVN repo custom SVN Symbolic Rules - 'Add' link disappears

Add/del links disappear when setting custom rules for Subversion repository in repository setup -> SCM details -> SVN Symbolic Rules.
When you click the link to add new field a new empty row is added below current one. Current row 'Add' link disappears (the one that was clicked), the new row has 'Del' and 'Add' links available.
You cannot add new row below old 'current' row.
If you delete newly created row, the 'Add' link is still unavailable, so you cannot delete and add a new one.
If you add and then delete all added rows, you end up without possibility to add a new one.