Susan,
 
You are right.  The Bitter Apple is supposed to be sprayed on what you don't
want them to bite/chew.  Used that way, the alcohol evaporates fairly
rapidly.  Some may learn to associate the smell with "don't touch" but in my
experience, they don't mind digging where it was sprayed, or using that
location as a litterbox.  No bad taste to deter them.
 
What, in my opinion, is really misuse is spraying it in their face.  Can you
imagine how that alcohol must burn their eyes?
 
On corner litterboxes.  We use a lot of them with no problems.  Perhaps
yours was too clean and your ferret thought it was a sandbox?  A little bit
of old waste from the old box might teach it what it is supposed to be used
for.  Otherwise it's an "oh well".
 
Dick B.
[Posted in FML issue 1535]