In the past (long ago), it used to be that any mixture value below 0.5 would cut off the engine. This was Austin's simplified model for "low/high" idle in turboprops...but when that model was created, Austin did not really consider fixed shaft turboprops and was essentially working off of the PT-6 paradigm. Now that has been enhanced to be more flexible, but still the "mixture ratio" really represents the fuel reaching any engine and not necessarily the "mixture lever position"...so it is applicable in the "stochiometric" sense though not so much in the "typical nomenclature" sense.
or maybe a broken simulator? If you did this in the same "flight session" without reloading the aircraft, then it wouldn't surprise me if it did not work. I myself have been very guilty of this during testing, forgetting to reload the aircraft and stuff not 'binding' causing me to chase phantom bugs. When a plane loads, a whole lot of initializations and "bindings" take place....and the only way to get a really clean "reloading" of an aircraft is to reload it via the developer menu, or restart x-Plane. The nominal way for us developers is to use the developer menu, but for end users, that's a bit odd and so many times, they just restart "the flight"...which does not always initialize everything properly in my experiences. (which is why the reload aircraft menu item was added I think).
I will say I have not seen the "one engine won't start" bug in a long time. IIRC, it happend mostly when attempting to restart an engine after shutdown in the same flight session and every single variable that should be 'set' to indicate a running engine was set properly. It was/is enough for me to think X-Plane has an issue but in order to take that to Austin, it needs to be 100% repeatable and narrowed down to a smoking gun config, or else Austin won't really look at it because I control so much with a custom plugin...and when we do that, Laminar tends to "wipe their hands clean" of any issues.
I won't lie, the Bravo hardware has been a major PITA for me. Here's the funny part....hardware setup has been a PITA for Honeycomb too....I spoke with the CEO at Oshkosh last year about it. This is exactly why they provide the profiles they do, in an attempt to alleviate the burden of a confusing setup from the end user, but in doing so, they end up providing "opinionated" configurations that cause issues with the Moo.
-tkyler