Thanks, but I don't think it is a question of bad html within the module that I am trying to add to the page in question since the problem is not related to a specific module but rather to a specific state of the page upon which I try to add a new module.
At this time I have tried with two different modules a custom made and a commercial one, Live Tabs from Mandeeps, both turned out the same way. But taking your advice I will try out with a couple of other commercial dnn modules like EasyDNNNews for instance and see whether that changes the procedure.