I really appreciate it. Thanks!
I edited the first post to make it clear. The board tends to rock vertically.
I already try to be as light as possible, especially with the front foot, so I think it's actually a flick direction problem, but I didn't find how to solve that. I also tried to think 'ollie', but the same thing happens.
If it doesn't get better in a near futur, like you said I'll probably put that trick aside for a moment and think about other stuffs, and sometimes give it some tries to see how it goes.
Footage is probably a good idea but I'm really not used to do that (filming, editing, uploading...). If I find the time I'll maybe do that.