When you export data of a goal report in a format (CSV, XML, …), I saw that the data download are the total of all the goals set and not only of the goal report viewed.
I find that this problem is due to the fact that the parameter &idGoal=idOfTheGoal (idOfTheGoal depending on the goal viewed) is not present in the different export link (CSV, XML, …) on each goal report.
I saw this problem in 0.5.5 version nevertheless it is is also present in the last version of Piwik 0.8.
API outputs should include both general goal stats and specific stats for each goal. There is no way to restrict an API response to only contain a specific goal data.
Thanks for your answer nevertheless as I specified in my post, when adding &idGoal=idOfTheGoal (for example &idGoal=1 for fisrt goal) in data export link we obtain a data export restrict to the goal 1.
And why when on a goal stat we click on link export as image, we have only the data of the goal whereas when we click on Export as CSV we have the total of all goals ?