when setting default messaging for patron categories it doesn't save if you choose digest, you have to choose email and digest, but there is no error to tell you that's what's happening. also i think if you select email and digest you get 2 messages instead of just the digest, but that might be another bug. Either way we need to make it clear why the messaging preference wasn't saved or add a note that both email and digest have to be checked for it to save. See: http://screencast.com/t/gA9v3qmYas
Btw this happens in 3.8.3 and master.
*** This bug has been marked as a duplicate of bug 6515 ***