The type of heater doesn't matter any heater can burn. There are a huge range of things this could be a burn is the most obvious. You need to know your temps! Just using bulb and guessing is not enough you should know the air temp inside the enclosure (74ºF is a min suggestion) and a hot spot temp (90ºF is a typical one cooler for baby ball around 88ºF) and a surface temp on the cool side (ideally around 80ºF)