It is with a twinge of regret that we have had to patch out the ability for players to double-jump. While this undocumented feature has been known about for quite some time, we originally decided to keep it in as a fun little secret mechanic that did no real harm.
However, it became apparent that this effectively broke the challenge of many of the levels, as almost all regular walls and fences ceased to become any sort of obstacle at all.
Thanks to those diligent players who raised this issue!