Cerveza beer kit - Weird foam?

I am a beginner and am brewing a cerveza beer kit from a can (hopped extract). I used the enclosed yeast and corn sugar. It is fermenting rapidly in the primary, but am getting a weird sponge like cake peices of yeast on top of the foam. Is this normal for cervesa's or what did I do wrong? I've brewed about 3 or 4 batches of ales from a can and had no problem but this is my first cerveza!