The current issue of American Rifleman magazine has an excellent (and lengthy) article covering the Kel-Tec RFB & RDB rifles.
I do believe you are correct. If the bolt carrier doesn't have enough speed to clear the ejection port from low gas, the fired case will be retained on the bolt and jam the new round as it is picked up. More gas will allow the bolt to fully travel to the rear, ejecting the fired case, as it should.In the write up the reviewer mentions the gas malfunctions he had then mentions that a double feed wasn't gas related. My understanding of the design is that it would be. Yes, no?
It seems to me that if the bolt travels all the way to the rear, the spent case is ejected and can't be there when the live round is picked up. More gas makes this happen. Correct?
I'm liking the RDB more and more over the DT MDR.