Exactly. The panoramic roof was the largest available on any car when it was released (though that record was quickly eclipsed by the Lincoln MKZ). It was engineered and manufactured in-house without the design input or subcontracted manufacturing by 3rd party sunroof suppliers that most other carmakers use.
There were reliability issues right from the start. As mentioned elsewhere in this thread, rattles, high-speed wind noise, water leaks, chattering during open/closing, failure to open, seals peeling off... Plus it wasn't designed to be repaired, so parts have to be destroyed to get access. Even routine maintenance was a problem (blowing out the water drains from the top with compressed air loosens the drain hoses and causes new leaks, and an ultra-expensive speciality grease is supposed to be applied all over the guides annually).
They did this already, with the 2nd generation design in 2015. It was somewhat more reliable and was also easier to repair when things went wrong. It looks almost the same as the 1st generation from outside the car, and internally isn't all that different either--there's only so much they could do without changing the body design.
For this reason, I suspect that we won't see a sliding roof again until the Model S gets a major redesign.