Installing F11 from March 23 on the custom partition screen in the box at the bottom I selected and already existing LV (which is displayed under the already existing VG) I click delete. It brings up a confirmation box to deleted the entire VG. It could do any number of things which would make more sense 1) grey out the delete button 2) just open the VG edit dialog 3) only delete the LV, not the whole VG 4) something I haven't thought of. But confirming the deletion of the entire VG when I only have one LV selected is bad behaviour.
This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle. Changing version to '11'. More information and reason for this action is here: http://fedoraproject.org/wiki/BugZappers/HouseKeeping
This is fixed for f13. It is present in rawhide. anaconda-12.33 and over will contain the fix.