Zanata's GWT resources had no cache headers, which meant that browsers could choose to cache items which should not be cached
Random editor problems (mainly on testing machines which redeploy more often than production)
Cacheable and non-cacheable GWT resources now have the cache headers recommended in the GWT documentation.
Once the resources with the correct cache header have been loaded by the browser, it should avoid the random editor problems in future. Users will still need to force a browser refresh (or clear cache) if they have old data cached with the old headers.