Jittery audio making lmms unusable

Having trouble with LMMS? Ask about it here.
On windows xp using the latest version of Lmms.

If I record a midi track and assign it a vsti, when I press play and drag a gui on the screen, the audio goes mental.
Same result if I use a native plug, or samples in either the song or beat editors.
So what's going on? This is crazy, no?

It makes no difference if I select the smallest or largest buffers in the audio setup, it still happens.
Does anyone else suffer this fate? Or it it only me?

On any other music app I've tried this activity doesn't occur. I propose it's to do with my other programs using asio4all.
Is there a problem with the program, the audio engine, both or none?
1. if you are using asio4all in another program, it locks your sound card so that no other app can use sound.
2. your CPU may not be able to keep up with the vst you have loaded. what vst is it? Have you tried using a different instrument in LMM?