Nothing specific to hiding/showing icons in config of Moodle but it does have to pull in code if using YUI combo (or might) and all Moodle 2.x's now do a ton of caching.
Check to see if designer mode is on in themes. If on, turn it off.
Suggest purging the cache on server and on workstations might resolve the issue.
If that doesn't clear the issue, turn on debugging to see what (if anything) Moodle reports.
'spirit of sharing', Ken