When I browse my rigs and press 'Delete' to get rid of unwanted rigs - it sometimes works - just deleted the rig and I can continue to browse.
Sometimes it seams not to delete anything, or jumps out of the browse-mode or hangs totally (either I have to press 'exit' several times or to reboot the KPA).
It seams to work best in case I press delete - wait - press ok . wait.
In case I press anything while the KPA is still deleting - then it leads to problems more often - but it does the same as explained above even when I wait (but not this often).
I use the latest beta version and have about 420 rigs in my KPA.