Probably, all the strangeness is hidden in the algorithms for performing a weak and strong jump. After playing for a while, I still can't predict exactly whether the jump will be weak if the run-up does not exceed a couple of steps.
Thank you for your feedback. I was trying to keep the jump close to real where the character comes to a stop for a second, aims to jump then jumps. I think the weak jump is happening because of a keypress during the jump. Its because if you changed your mind and you pressed jump you can quickly press left or right arrow key to cancel the jump. However for any other weak jump I am working on the code. Hopefully this will be fixed. Thank you again for your feedback. ;)