Think about it. If your already using ice in your bong and you put a lighter to the bowl (lighters are much hotter than tap water) why wouldnt it break then but it will with hot water? I know its not exactly the same but if you have ice in the bong than in a few minutes the stem and slide will be just as cold as everything else, then you put a lighter to it. If a bong will break with hot water and ice then it would also break the slide every time you use ice and try to light your bong. It doesnt happen unless your glass was annealed improper.