I think I've relied on undefined behaviour when styling the flags so far, and it mostly works everywhere, but I guess still there are cases where it is broken.
I tried this out in other browsers (Firefox and Chrome) and experienced the same issue. I'll reach out to the friendly web designer who developed the CSS for the metrics website before we added Relay Search and ask if it's an easy fix. I somehow hope that it's just a matter of setting a min width for the flags column, but before I mess with this myself I'd rather ask someone who really knows what they're doing.