I just noticed this about deltaclip~, when a patcher wasn't working as expected: the output of deltaclip~ is clipping signals at zero (does not go below).
The MSP Reference Manual says of deltaclip's output that "The input signal is sent out, with its change limited by the minimum and maximum slope values".
Easy to check this: open the deltaclip~ help patch, and change the "zero" number box at the top to the value of -1.
So, bug or feature?
PS: I tested this in both Max 4.5 and 4.6, both on OS 10.3.9, and the results are the same.
Also tried with Max 4.6 on OS 10.4.8 - result was the same there too. In addition, I had to remove the delta~ object from the deltaclip~ help patch on that system, because otherwise Max would crash as soon as I started audio processing.