Bug when I use AJAX POST?? I didn't find any solution, help

hi all, when I try to send a data with "POST" method to a php file, like:

URL:"phpfile/MAKEJSON.php"

DATA: "c2array="&myarray.AsJSON

my php file will write a new file:

$myfile = fopen("users/$id/$namesavegame.json", "w") or die("Unable to open file!");

fwrite($myfile, $c2array);

fclose($myfile);

and this work, the problem is a result of the json file:

{[/b]"c2array[/b]":true,[/b]"size[/b]":[412,5,1],[/b]"data[/b]":[[ you can see, "\", and i don't find any solution about this, I don't understand why "[/b]" will appear...

with GET is working good, ( {"c2array":true,"size":[412,5,1],"data":[[) but I need to use POST....is a bug? thank you very much... I don't know how to solve this problem...