Nice one button game!
Unfortunately spacebar didn't work for me pretty often.
Maybe I'm wrong in your situation, but I had similar problem. Maybe you read OnButtonDown() of Input in the Update() and write the value to some flag for the dash request. Then it may be overwriteen in the next Update() before the dash was performed. If that's the case, you can reset the flag only on next button press and drop it just after the dash performing.