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That means what? That it is enabled?
If you enable caching, the javascript file that controls the drop-down menu and category display etc. will not be included on cached pages and it will look bad.
Solution: Disable caching for this module (you can still leave it on for individual blocks from the module)
Long-term solution: In XOOPS 2.1.0 we will have a solution to this problem. Unfortunately, modules will have to be changed to take advantage of it, but it will be a very simple change.
With that said, you should note that the caching stores the output of the module content and therefore, if you enable caching and go to the module, what you see will be cached. The next time someone accesses the page, the cached version will be displayed - but this may lead to forums being displayed to a user, he should not see due to permissions, or the user will see edit and delete buttons where they shouldn't. Again, XOOPS 2.1.0 will have something that gives the module developers something to use to solve this problem.