Did we ever figure out what caused certain shaders to distort?

I remember a while ago (6 years, in fact; time sure does fly) posting about an issue with the Background Offset shader blurring horribly, even with a simple pure red/green stripe:

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As far as I'm aware a few other shaders also did this (some out of the photoshop pack). Is there any fix to this? I recently came across a situation where i'd like a nice "underwater distortion" effect and while 2 perspective objects layered work, it's an ugly solution. Thanks.

EDIT: a lot of shaders seem to not work with "premultiplied alpha" checked?

Bumping this because I'd like to know what's going on here.

[MENTION=10153]NaitorStudios[/MENTION], I see. If you know how this could be done, let me know. I did not see anything to change that affects the amount of 'samples' within the shader.

What's curious however is I seem to have fixed the problem by using different colors than Red and Green, which the shader is supposed to use and is even referenced in the code.

Using (blue 0,0,255) and (fuschia 255,0,255) causes it to work correctly; at least on my main and secondary machines.
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Looki's Background Offset shader. It takes the red and green color values out of whatever image you apply the shader to and modifies the position of the background behind it, kind of like a special lens. By different colors I mean instead of using red or green (which the shader offsets the background with, Red for X Green for Y, this can be found in this shader code itself) I used blue and fuschia. For example, when the shader works as it says it should, the image for a distortion effect might look something like this:
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but using this, it will either blur horribly like the image in my first post, or do nothing at all, seemingly at random. Tinkering around, I managed to get it to work as intended (smooth distorted background) using an inverted version of that image, which makes no sense considering how the shader originally works (supposed to only use R and G values to change background):
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And the shader worked properly when it came out quite some time ago, so I imagine something changed in fusion builds that affected it.

The shader file i'm using is the updated one converted to DX11 by pixelthief, which can be found in the "converting shaders to dx11" thread. The problem existed in the old dx9 version of the shader too, at least for me and a few others.