--prune-empty-dirs option not doing the job

[js_spamfree-rsync at yahoo.com]

Hello and thanks to all who so generously assist on this great list.

test command:
rsync -avm --del --prune-empty-dirs --compare-dest=/Users/generic/Desktop/B /Users/generic/Desktop/A/ /Users/generic/Desktop/C

produces a large number of directories and nested directories on the destination that are empty.  i've tried tweaking so many different combinations of options i'm beginning to lose track!  none of them produce the proper result in the destination directory.  

does anyone have any ideas?

many thanks, and the feedback is greatly appreciated.

--john