Towel Rail Heater

I recently replaced my old electric heated towel rail with a tall towel rail radiator, plumbed into the central heating. In case I want towels dried when the heating is off I also fitted an electric towel rail heater element, a tubular heater that goes into one of the valve holes in the radiator. The new pipes had to run under the floor so they come up vertically into the radiator. This meant I could not readily mount the element at the bottom of the radiator with a tee for the water connection. I was not sure how you would arrange a valve with such an arrangement in any case. It therefore seemed sensible to mount the element at the top of the radiator in place of the supplied blanking plug i.e. like a normal cylinder immersion heater. When I plumbed in the radiator I initially ran it with the central heating but when I went to bed I turned off the heating and turned on the electric heater to try it out overnight. I woke up at about 4 am to total darkness, my LED alarm clock was not on. I tried the bedside lamp but that was similarly dead. On investigation I found the sockets MCB had tripped. By a process of elimination I traced the fault to the new towel rail heater which was shorted to earth.
I’ve now looked at the instructions 😳 and it says:

“. The heated towel rail must always be mounted with the element at the bottom with the heated towel rail in the upright position. Failure to do so may result in a fire hazard.”

This statement is actually ambiguous but by bottom I think they must mean the appliance goes on the bottom of the radiator rather than the element end of the appliance being at the bottom and the cable end at the top. The heater is a sealed unit so I don’t know what kind of thermostat is used. I’m wondering if this is some kind of bodged design and the heater is intrinsically unsafe.