Steps to reproduce:

1. Open "Java Control Panel" General Tab
2. Click "Settings" in the "Temporary Internet Files" section
3. Press "Delete Files"
4. Click "Ok"

The ok button does change from light-medium blue flashing to a slightly darker blue when clicked but the shade and action is very ambiguous, basically appearing almost as if nothing has happened. There is no indication that the cache actually clears or is clearing, the dialog box just disappears. This can appear to be hung over a minute if the java cache is full.

There is no progress bar, spinner, or other indication that "something is happening".

This is a hostile user experience when the disk I/O from clearing the cache starts to take more than a second (which can frequently happen when the cache is large, and the machine is otherwise under load).

The most likely scenario is that the user thinks the Java Preferences Dialog is broken, and kills it while it is still emptying the cache.