Squat knee buckle

you just gotta keep your ass under you when going up. notice how your hips goes up first, it makes you use too much back in the exercise

try putting your feet forward and a little better stance

I have the same problem, but actually more severe, i go right over to one side and apparently looks like i'm off balance. My friends cringe when i do it.
Might help you to make your stance less wide.

Hope you've corrected it, it's a common flaw and often is caused by tightness in the hips and/or ankles on the SIDE YOU ARE MOVING TO. If you've not sorted it, find a GOOD strength coach, physio or personal trainer to see which muscles are tight and which aren't firing. Some temporary isolative work and deep tissue massage solves the problem in most cases. Good luck!

Interesting, i didn't realise that was the cause. Thanks, will do.