Saved image does not match viewport image

I was going through the intro to shaders tutorial and I wanted to save an image to mess around in photoshop, but I keep getting this messy and weird result that does not match at all what I see on my viewport.

It looks like the buffers where not properly cleared and still had data from past frames, but I don’t really know. I tried saving to jpg and png, using img.grabscreen(), ofSaveScreen(), but it still gives the same result. Any idea of what might be the problem?

This is what it looks like taking the screenshot using windows printscreen