In the current betas there is a known issue where image effects do not work with single-pass rendering. After talking with some other devs, there was some discussion that it may not be possible to make all image effects work with single-pass stereo without significantly re-writing them.
Could someone from Unity let us know if there are plans for a general fix for the issue, what that will cover and what beta number it’s likely to show up in? That’d be really useful 
Do you have some examples of it not working? Generally what’s required is that you use the TRANSFORM_TEX() macro when sampling from a stereo texture.
For example, if you have a sampler2D SourceTex; you will also need a float4 SourceTex_ST; and you should transform the texture coords like this: TRANSFORM_TEX(v.texcoord, SourceTex).
We’re still fixing single-pass stereo issues, but it’s unlikely that all image effects will work out of the box, because we use two textures packed into one.