It seems that there is a bug with Cairo's bypass automation. I was using Sylenth1 and having automation of gating speed of Cairo. Then I added another automation of bypassing it but the audio kept jamming. As long as I continued the playback the audio was stuck all the time. I changed to another synth but the problem still occurred, until I turned off the bypass automation.
Btw I'm using Cubase 5 x64 on Windows 7 with Firebox.