You were right. By holding each key down until it beeped, I was able to play consistently. Still ran into a show-stopping bug right away: bought some wares, jumped to a nearby system, sold them... but the game continued to show my cargo hold as 3/4 full (even while correctly listing no content). So I was unable to buy more cargo for the next jump.
In related news, it looks like you never implemented fuel consumption and refueling. Is that correct?