I can't seem to replicate this at all (and the code for that ability doesn't actually affect the floating strings so I'm not sure how that would correlate to a crash in the first place). What OS are you running the game on?
(I tried to insert a gif of myself using that ability on the floating code string, but the gif was too large to insert)
I'm not too sure what to do about this bug if I can't replicate it.
Secondly, if you hit ~ a "Feedback" button appears where you can submit formal bug reports.
Thirdly, the ability for double jump explicitly says the base double jump is automatically equipped. The upgrade, the Rocket Jump is equipped via ZXC
