Actor jumps differs in height.

Alright, I give up, I need your help. For many of you it's probably a very basic task, but I can't get my actor to jump uniformly. If I hold Space for him to continue to jump, he jumps different in height. Sometimes he jumps correct, sometimes a couple of pixels to low, sometimes a couple of pixels to high and I have no idea why.
Any help is appreciated. I've gone through all of the tutorial examples for jumping, and I ended up with this.
http://www.fjant.se/temp/wip/games/jump_rule01.png
http://www.fjant.se/temp/wip/games/jump_rule02.png
*Edit
No way to show images directly in the forum?
Any help is appreciated. I've gone through all of the tutorial examples for jumping, and I ended up with this.
http://www.fjant.se/temp/wip/games/jump_rule01.png
http://www.fjant.se/temp/wip/games/jump_rule02.png
*Edit
No way to show images directly in the forum?
Comments
Here's a simple demo I made a while ago that might be of help - http://gamesalad.com/game/3247
Yeah, your solution seems rock solid.
Here are the images.
http://www.fjant.se/temp/wip/games/coa/jump_rule01.png
http://www.fjant.se/temp/wip/games/coa/jump_rule02.png
Thanks for the tip, I'll get right on it and try out