folder->messages(begin, end) implementation on maildir

I'm getting some strange behavior using the "folder->messages(begin, 
end) construction. I can work around it, but I think it may be a bug.
Let's say I have exactly ONE mail message in a maildir folder ($folder). 
(The message is in the "new" maildir subfolder, and nothing is in the 
tmp or cur subfolders). The following code:
   my $n = $folder->messages;
   print "cnt=$n\n";
   $n = $folder->messages('ALL');
   print "cnt=$n\n"
   $n = $folder->messages(0, 20);
   print "cnt=$n\n"

Produces:

   cnt=1
   cnt=1
   Use of uninitialized value in concatenation (.) or string at 
./testprocess.pl line 54.
   cnt=

Line #54 is the last "print" line (print "cnt=$n\n").

Similarly, if I use @emails = $folder->messages(0, 10), I get an array 
of size=2. If I loop through the messages using foreach, the loop will 
process twice and the $message object in the second iteration is undefined.
If I use $folder->messages('ALL') or any other construction, this works 
fine.
Mike