This was reported as a C2 bug and not a C3 one. Also I think tagging the devs in posts in the bugs section is kind of redundant.
Anyways, what's happening is the textbox object, once selected, blocks most all input events from passing through it to anything else. So the keyboard state (which is stored in a array in the keyboard object) isn't updated when the spacebar key is released.
I'm not the developer, but you can make the keyup events not be blocked from the textbox object as a self fix. It would make the key released triggers fire as you type stuff, but perhaps that's acceptable in your case.
Anyways, set the textbox id property to something like "foo" and then using the browser object run this code:
start of layout
-- browser: execute js: "$(document.getElementById('foo')).off('keyup');"
I don't think it would work in C3 unless jquery is used in the textbox object.
Alternatively, I guess if you wanted more control you could just do your own textbox with events and filter keyboard events yourself. Last I checked the keyboard object wasn't quite up to snuff to get typed keys with case and such, so you could capture keys with a little js as well. I thought I had posted this before, but I guess not.