WinCvs 3 way diff with the "-3" option?

Question

I'm working on writing a Perl script that provides an interface to WinCvs for all of my Perl scripts to use. While trying to implement the diff command I came across an option that looks incredibly useful (if it does what I think it does) but I can't figure out how to use it.

Here is the "usage:" output for the WinCvs diff command.

My question is what is how do you use the -3 option?

The online CVS documentation doesn't even reference this option and I can't figure out a way to make it produce a useful output.

I tried using it like this cvs diff -3 -r<revision1> -r<revision2> -r<revision3> but I just get the following error.

Using this command with only 2 revisions seems to give the same output as if I didn't use -3. Am I missing something? Or is this command just inherently broken in WinCvs?