Yep, that's defiantly it :)
Jumps are usually GetKeyDown, not Up.
I understand the need for it with high/low jump, but u should be able to implement it with down on jump and on Up check the state.
I'm not sure exactly what you're suggesting but I've had a fiddle with the jump today and I think it feels a little better now.
I really want to keep the jump on key-up as that produces a need for timing when you want to do a big jump. I also prefer the hold/release mechanic of wall jumping.
What I've added are:
* A micro-jump on key-down that blends with the main jump if you tap/release the key quickly. You can just see it when you hold the button and the character goes into a crouch (which just looks like 'animation' in that case) but does mean that the character's jump technically begins on key-down now.
* a subtle sound effect on key-down, adding a modicum of feedback.
* a fraction of leeway with checking whether you are on a platform, meaning slightly late jumps are registered.
I've uploaded the WINDOWS build to v0.2, alongside the jam entry version, if you fancy giving it a try (absolutely no worries if you don't, ofc :D
Cheers!