Yes it is normal for that to happen with the foaming. When adding sulfite always dissolve it in a littke bit of water or extract some wine, dissolve the S02 (sulfite) in that and then add ir back as adding a solid to a wine with some C02 in it will give the C02 a solid surface for the C02 to come out of suspension and it can get very messy and we like to call it a wine vlcano as sometimes it can seriously over flow your carboy!!!!!!!!!!!!