User Agents used to work correctly before the upgrade. I can now see the following bug:
1. Enable user agents and use the default high and low groups.
2. For any particular page, ensure there are no caches created yet.
3. Try to access the page using the latest version of Chrome or Firefox on the desktop.
4. An index.html file is created.
5. Try to access the same page using an iPhone 5.
6. The same index.html is returned instead of a new file index_high.html being created.
Note: If you do this the other way around:
1. Access the page using an iPhone first.
2. An index_high.html is created.
3. Access the page using Chrome/Firefox on desktop.
4. An index.html file is created.
Then everything works fine.
Please investigate :-)