GrabPass Textures flipped

I'm currently using GrabPasses for several screen effects in a title I'm developing. The issue I have at the moment, is that when I use more than one texure using a GrabPass, such as the Bloom screen effect and my own shader using a grab pass, the result of my GrabPass shader is flipped upside down.

I am not using AA in any quality level in the project, but I have tried using:

 #if UNITY_UV_STARTS_AT_TOP
     if (_GrabTexture_TexelSize.y < 0)
         o.screenPos.y = 1 - o.screenPos.y;
 #endif

I have also tried using named textures in my GrabPass to treat it as a separate texture, but neither of these things work. The only process that does seem to yield effective results is by using ComputeGrabScreenPos() rather than ComputeScreenPos() but this causes a nasty blurring of the texture. Is there any way to get around these issues?

Any thoughts would be greatly appreciated.