it will basically be the same deal as that discussed in the "carezza" thread and that is, that when the machine is switched over to produce steam for the steam pipe, there will be a build up of extra pressure and this ***usually*** results in some dripping/steaming in most machines of this type.
The discussion then can be narrowed down to...how much of this dripping is "normal", and for any individual machine, when does the dripping become too much. So unless someone here has exactly the same model machine and can advise you, or you telephone the nearest agent for the brand, you might never find out what is "normal" for the model.
It then will come down to managing the situation, which would be to start using the steamer as soon as practicable. This should stop the problem from occuring because the path of least resistance should then be for the steam to exit from the end of the steam pipe and into your milk, instead!
Sorry cant be more help.