I bought a Fulham Racehorse RHA-UNV-254-LT5 electronic ballast for a light box that uses two FT36W/2G11 lamps (Also know by the Philips name "PL-L")

The picture in the listing states that in can run those type of lamps, however the one I received only says FT50 or FT55. I wired it up anyway and it is working fine and the input current (Measured by a P3 Kill-a-Watt) is right on target with the spec sheet for the revision of the specs that used to list the FT36 (A PDF file that I saved a while ago) 

I searched the model number on the Fulham website and even it only lists FT50 and FT55

I am confused as to why the FT36 was removed? It seems to doing fine (Temperature wise and input current as per the old spec sheet) and the lamps seem happy and don't look over-driven so is this a reason to be worried or is this fine?

PS: I only replaced the ballast as I absolutely hate instant start fluorescent lamps and I was told Fulham is a good brand

I attached a picture of the ballast label from the eBay listing and the old spec sheet

Thanks

Possibility coming to my mind, neither really thoroughly supported:
1) The ballast shall shut down an EOL lamp, which may melt the socket. But when just single PLL-36 is installed, the ballast may not be able to reliably distinguish EOL on such low voltage drop lamp and continue to operate it, so damage the socket. But that won't explain, why operating two PL-L36 in pair (so equivalent of 72W) would be problem, but a single 50W won't. Maybe if the ballast can not operate it single, they do not want to specify that type at all.

2) The voltage across the lamp(s) during preheat phase is too high, so a premature (cold) ignition with consequent diagnostic malfunction (ballast won't recognize the ignition had already happened and so does not move in the operation state machine; problem for e.g. IR21592 controller) may happen. Here the series connection won't help, as if the voltage is sufficient for single lamp ignition, it ignites via the capacitance towards ground, so lowers the drop to fraction of it, so the second lamp ignites as well.
However I have not seen other controller than the IR21592/21593, with ignition detection method, where that problem could happen (and really be a problem except a bit shorter lamp life)