Kinda reminds me of my experiences at HEL when checking in for a EasyJet flight to LGW after the first week of operations. They check in lady insisted on a passport even though I tried very hard to convince her that my official ID card was perfectly fine for travelling to UK, non-Schengen and all. She wouldn't budge even after I argued that I'd made it through UK immigration dozens of times with that particular card. I had to surrender and show her my passport as the queue behind me was getting impatient.

Of course I made it through border controls at both ends with the ID card without any problems.

A couple of weeks later for the same flight they accepted my ID card just fine...