[AS2]Help needed with POST

Hi, guys, any help will be useful
I`m trying to send variables to php script via POST with AS2. This is the code I use:

var sendvars:LoadVars = new LoadVars();     
sendvars.at = 'abv';     
sendvars.wpc = 'abv';     
sendvars.AlbumName = an.text;     
sendvars.send('http://www.some_url.co./login.php', "_blank", "POST"); 

the variables are sent, but POST is converted to GET and flash open this URL: http://www.some_url.co./login.php?at=abv&wpc=abv&AlbumName=something

so, any ideas why is that?.. as2 bug or something else?