How fast is your internet connection ?
Does it happen all the time ?
Have you tried clearing your cache and then visiting a wiki edit page again ?
The WYSIWYG editor the wiki is using is called xinha and it's a lot of javascript that needs to get loaded as the edit page is loaded. On firefox and IE I get a little delay as it tries to fetch all the icons and stuff.
I don't think the internet connection is the problem because it's a local installation. Besides, the bug happens in a local sever and in my local installation.
And yes, it happens all the time (when you click on "edit" for the first time).
I also tried deleting the cache but I get the same result.
Maybe is the version of the XYSIWYG editor?. I'm using the branch oacs-5-2 (even though for the xowiki and xotcl-core packages I'm using the branch HEAD)