Thanks a lot! :D
I uploaded the game with very good controlls, but decided to change some things with the sprites, and today I found out why everyone dislikes the controlls after the update: Odd locations of pixels in the mirrored sprite's mask...
Thank you for the suggestion!
I used GMS 1.4 and yes, I do know Shaun Spalding. In fact, this is a script I wrote long ago by him, but I decided to rewrite it.