Thanks for your nice comment! :)
The jumping bug is because the player can always jump while the cat is colliding with the map. The jump then ends as soon as the cat "re-collides" with the map again. Therefore it's possible to jump right again.
Maybe we'll improve on the whole game, but it needs a better engine as a base. This was my first attempt of writing a little 2D engine and it served perfectly fine as a learning project, because I learned what to do differently next time ;)
Thanks again! :)