Franko75,
I've not been through yout javascript in detail because from the symptoms you describe, I think the (main?) problem lies in the php not javascript.
If the same php script is serving up the form and a response to some user event (submission or whatever), then the php must contain two (or more) main branches - one to serve the form and one to perform an action and serve a response.
From the symptoms it appears that the form is being re-served when an action/response was demanded.
This situation can be handled by including an "action=xxx" value in the post/get data. For example, initially, action=blank would cause the php to serve the form; action=1 would branch to eg. a form checking block (or whatever) with appropriate responses; and similarly action=2, 3 etc. would branch to further other actions/responses. I normally handle such branching in a switch/case structure.
Alternatively, of course, you can have each action in a separtate script, but I find that a bit untidy. Some will disagree - it's really a question of preference.
Of course, it may be something else, but that's what first comes to mind.
Airshow