I keep having this glitch show up while zooming on still images.

I'm trying to edit simple, pan-and-zoom style, montage videos, and this recurring glitch is ruining my efforts:

In short, I place a large image on the timeline. I zoom in toward the center. Before and after rendering, the frame keeps abruptly shifting.

Anyone know what this is called? Or why? Or a fix for it?

Any suggestions are much appreciated!