Ediff misbehaves

I have a problem with ediff - it take a very long time to process
regions and come up - sometimes it'll never finish which leads to a
"hang".
While it is processing it consumes huge amounts of CPU time - the whole
system gets to its knees.

As an example that hangs every time - ediff two identical buffers.

Any ideas what's wrong with ediff and how I can get to to work properly?

Dan