I made some changes  to ovirt-engine that make it now more aggressively (and correctly) cache all static assets. We were previously caching some things, but not all. (Thanks to ykaul for noticing.)
The upside is reduced server hits and faster page loads.
The downside is you'll have to clear your browser cache more often as you are developing. (You can use a browser plugin, incognito mode, F12 > disable cache, etc. if you don't want to keep opening the dialog.)