Not a glitch, but probably an overlooked consequence... 0 aircraft limits on cities would exist at such an early stage of the game due to no buildings offering any aircraft capacity. Huh... that's kinda funny actually. I wouldn't have thought about that until it was brought up like this either.
So I guess that means we need something to accompany the ornithopter that gives aircraft capacity (or if there's an override setting in the xml - the old hunter's hawk never seemed to have that problem?)
Maybe there should be an Aerodrome Clockpunk building which gives air capacity.