IMHO
Don´t worry about the divided by 2, that I guess is only for heavy load games.
What I suspect, is that is an issue with the nearest neighbor routine when doing zoom and rotation.
We got that on Deluxe paint and we have it going on photoshop nowadays.
It is a fast routine, not perfect, so to feed it correctly there must be a central pixel, so it divides the image into 4 zones to produce the operation.
No central pixel, you get garbage or it kills some line.
I have that issue when working with photoshop, even when using x2 stuff.
Since it is open gl and GLB is open gl, I suspect it feeds on similar source.
It is a fast routine though.

My babling is not GLB related but a theory, I would have to test to figure it out, but my work programs respond the exact same way as your original post, hence the reason I correlate the facts. I could be deadly wrong.

It is late today and I have seen to much computer work stuff

Will do some testings tomorrow.