I was just about to upgrade to v2.2.10 when I noticed my remote dropdowns where generating multiple hits to the server when no results are returned. It also looks like the caching parameter is ignored.

For some reason this bug only happens if you click on the actual dropdown icon (you will see the loading icon spin, stop, spin, stop... ).

If you look at the console log you will see multiple repeated requests.

http://jsfiddle.net/kmd1970/pzcm8zo4/
(Please note this link needs to remain http:// for the remote ajax call to work properly)

Looks like this issue started in v2.2.8. In more recent versions (v2.2.7) the dropdown icon doesn't open the empty menu (after load) until you click into the input at least once, so this issue doesn't occur.