Today I was about to change shockoil in my Losi Mini Eight. I started to fill up the shock with oil almost all the way up. After that I pumped up and down with the piston in order to get rid of any airbubbles. After that I screwed on the top and secured it tightly. However after doing this the shockshaft has been pushed all the way out and you can`t push it back in. It is locked. Why is it like this?

Also, after some attempts I was able to push it halfway in but not all the way. What should I do in order to be able to push the shock shaft all the way in?