I will file this as bug if needed, please let me know. However, I am checking if I am missing something fundamental.
I am creating a new shader and found that the pixelSize uniform was set to 0,0 when I applied the effect to a 'Text' object. I checked this through running remote preview and using spector.js to inspect the uniforms for the effect when the 'Text' object is rendered with the shader. When I apply the same shader to a Sprite object it works fine.
After seeing that, I tried some other built-in effects on the 'Text' object, to see if I could see a similar error. I found that when I applied 'Bulge' to a text object, the text disappeared in the editor. I then tried remote preview and spector.js with this and found that srcOriginStart and srcOriginEnd were both set to 0,0. So the bulge shader also 'failed'.
I found that the effects started to work when I stacked another shader (any shader) on the text object (so then there would be multiple renders to multiple FB and then the uniforms were properly set for the fragment shaders.)
Should I be doing something special with my shader to make it work with the 'Text' object? If there is, likely the same thing should be applied to the builtin Bulge effect also (and perhaps others?)
Here's the spector.js output for looking at the Bulge effect on the text object:
Thanks for the help 
Ashley!