freeze and bounce for K2 in sonar 4 don't work

i have sonar4 studio and kontakt2.
i did some test, using the big K2 library piano multi, with the convolution and the harmonics.
when i play the piano, i run out of polyphony and reach cpu overload very easily.
i was expencting that, running a freeze or a bounce track of the DXi synth, the track would be rendered in a good manner.
unfortunately this is not happening, because the audio track that is created has audio glitch and portion of silence and clicks.

what's happening? why this otpion doesnt' work??