Blender 2.71 - Compositing with openCL image tearing issue

I was wondering if anyone else is having issues with rendered compositing images having blocks of colour appear on random frames when using the openCL button activated. For that matter, do the opencl button do anything anyway?
I have a macpro 4.1 with NVIDIA GTX 680, Cuda driver 5.4.7. I saw a similar issue not so long ago with Autodesk Smoke and it ended up being a GPU issue with alpha channels not being dealt with properly.
Many thanks

I have only seen tearing in renders to video media, put it down to compression artefacts. Now I’m not so sure…

I’ve also had this. I know this isn’t the newest thread but with blur, I’ve had parts that just didn’t blur. I have 2 nvidia 760s…