Steve,
  Could you add a 4096 bin mode? I've got some great
burbling noises coming out
 at 2048, but I think the extra res. would make it even better. 
Check out the latest CVS... I threw it in for you ;)
Memory usage is a bit higher (but not by much...).
  I did once manage to get FT disconnected from jack
when changing bin sizes,
 but only once out of a few dozen changes, so it might be unrealted. 
Yes, I believe there are some buffer overrun gremlins hiding in there that
really only come out at those big FFT sizes.  I find that I lose too much
time-domain resolution at those sizes for anything with transients. It just
mushes right up.
jlc