[imp] Error - undefined index: showunsub

[Shannon Reall]

I have recently updated to horde 3.1.3 and imp 4.1.3.  Everything looks like
it is working fine.  The only problem that I ran into was when I was testing
some of the different options and set: Use IMAP folder subscriptions (under
Mail | Server and Folder Information).  Setting this, displays the error:
Notice: Undefined index: showunsub in
/path/to/apache/horde/imp/lib/IMAP/Tree.php on line 105.

Thanks in advance for any help you can provide.
Shannon