This is very specific and I'm wondering if it's a bug or an issue with my shader:
I have written a very simple Effect that modifies sampled pixel coordinates based on a predefined number of frames and displays them in a sequence - As an example, you set a single Sprite Animation Frame to a filmstrip with 4 frames, set the frame number in the Effect to 4 and speed to whatever, it will cycle the 4 "filmstrip frames" from the Sprite at the given speed.
The problem is when there is more than one frame in the Sprite Animation - the pixel sampling is completely wrong even if the Animation Frames have the same size - it seems to sample areas of the final Sprite Sheet instead of the Sprite's Animation Frame boundary (changing the Sprite Sheet size under Project Settings changes the sampled pixels - still wrong, but there is a distinct change).
I'd rather not share the Effect publicly until I have this ironed out but will gladly send it to someone with more knowledge to take a look if they are willing.
Does anyone have an idea what's happening based on what I wrote? Thanks in advance.