in filtergraph.maxhelp :
-> in the filtergraph inspector, go to Constrains MAXIMUM Frequency/Amplitude/ or even Q : set it to "" using delete key
-> save the patch
-> open it again
-> now you have Constrains MINIMUM set to and the number that was in the MINIMUM is now in the MAXIMUM...
We just tested that this bug happen in Max 4, 5 and 6...