Good timing, Hubert - I've just hung-up with an engineer working at the manufacturer of that ballast. He told me it already has a 5 ohm 50 watt resistor built-in circuit which is used apparently to fool computers by simulating the resistance of an traditional halogen bulb. This + a EMC filter (he mentioned capacitors?? RF canceller). The manufacturer also reassured us that there are both open & short circuit automatic protection that will trigger & tested within 1~2ms. So to him he is not too worried for your car
However he mentioned that whatever your problem is, to them it is not caused by their unit but more of an underlying electrical condition that your car (and some others apparently) is likely suffering of. That underlying electrical issue being amplified by the ballasts
Whatever that means mate. We change car?! I would mind a 3.6L fast Boxster
Like Dwight recommend, I'd still add some resistance on the circuit and see how things goes.