This reproduces consistently on my device. If I start with my device in portrait mode, then rotate to landscape and back to portrait, the page will be shown in the wrong scale.
Description
Event Timeline
My User Agent is Mozilla/5.0 (Linux; Android 5.1; Nexus 5 Build/LMY47I) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.111 Mobile Safari/537.36
Tested Nexus 4 with Chrome 40 / Android 5.0 then updated to Chrome 42 / Android 5.1, wasn't able to get a reproducible case. I do see it stick for like a fraction of a second, then it snaps into place each time for me.
We can't reproduce this on similar hardware/software, manage this stuff primarily with pure CSS (which makes it less likely that this is a bug we can fix), and it sounds like it's easy to avoid (don't do somersaults while using Phabricator), and to work around (reload the page). So we don't really have a path forward here, don't have a real reason to believe it's fixable, and the impact seems very small.