It's possible that the element has blown and ruptured, that would allow water in the tank to short the two exposed ends of the element and allow current to flow creating what is in effect an electrode boiler. The high resistance would limit the effect of the element, but as electricity takes the least path of resistance, would not necessarily cause a breaker to activate.
I have seen this happen in commercial and residential immersion heaters, and see no reason why it couldn't happen in an RV heater. If you have a multimeter, check the resistance of the element, it should be quite low. Also look for damage near the bend in the element.