Batch update of Communication preferences not applying changes when removing all options

To reproduce (have reproduced on Demo site

1. create profile with email & communication preferences fields done here if yr quick!
2. search for individuals
3. batch update via profile (communication preferences created @1
4. remove all preferences & hit "copy" to change all contacts
5. save

checking any of the contacts, the changes have not been applied

This could, of course, be intended, but is not in line with the rest of the system (I can deselect all options when editing an individual)