Problem can be seen here

The problem is in the tag <dmath> and not appears in <math>. By the way, we have seen some particular behavoirs of this bug: it appears in different type of web browsers but, magically, some people could not have this bug and see the page without these strange bars. (Maybe only the editors of that page could see this bug, I dont know)

It can be seen at this page:
http://it.wikitolearn.org/Analisi_I/Introduzione

In my browser and web page it appears, but, as I said, it can hide and sometimes it doesnt appear.