Dave Smith Instruments SYNTHESIZERS

I have had my new P.E.K now for almost three days and I love it. I 
have a few vintage analog sizers so creating sounds on the P.E.K is 
easy. There is only one thing that is a bit annoying. I don't know if 
I'm doing something wrong or if it should be like this: 

I don't know how to explain it but sometimes (quit often) when I hit 
some notes it seams to be a little glide on the sound. Like the pitch 
is sliding in the beginning of the note. First I thought I was running 
out of polyphony so I turned down the release on all envelopes but 
notes are still sliding. Why?? It is very irritating if you want a 
clean sound. (Yes I have Glide turned down on the oscillators.)

Anyone knows why the P.E.K slides? 

Kind regards
Demokid