I say all sounds from the Cakewalk Sound Center synth. But I have only tried 8-10.
Strings, horns, pads, leads. It is consistent and I don't think it is the sounds themselves. I might guess something in the routing, but it's pretty basic and simple insert of the synth. I wouldn't know where else to look.
Doesn't do it from Dimension Pro, Dropzone, etc. It doesn't seem to matter if I play them soft or loud.