Yeah, this is a known issue :)

Yes, silly camera panning input code things :)

This could be due to running on Mac, I've heard GUI matrices behave differently there! Are you able to test it on a Windows machine running the same Unity version?

It irks me too! It seems to be Unity doing magic in GUI.Window to make it easier to notice a change when selecting it. GUI alignment is in general a very low priority thing, but I will look into it in upcoming versions :)

(Just look in horror at the gaps under/around the 3D preview)

Do you have multiple monitors? If so, try putting Shader Forge on another monitor, and see if the issue remains. Also, try docking it instead of having it free floating

Weird bug :0

Does the error appear when creating a shader from scratch as well?

Are you running Unity Pro?