lestat,
This is actually a bug in Chrome which affects randomly some pages and some setups.
The bug is filed in
https://code.google.com/p/chromium/issues/detail?id=246875 and the discussion about it is in
http://productforums.google.com/forum/#!topic/chrome/zID6uQQfKH8.
Fortunately, some Chrome developers seem to have acknowledged that there was a change in the behavior of the browser with cached 304 requests which is exactly what we've suspected in our earlier email exchanges.
So if there will be nothing fixed in the coming weeks, we'll probably blacklist Chrome as unable to handle 304 correctly in the console (and probably in the Web sites even though this may cause us a lot of trouble with some customers.)