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)