PrintJob no margin info in browser

I’m trying to print a movieclip from flash. I’m using the PrintJob pageWidth and pageHeight properties to scale the clip to be as large as possible. Also, I’m trying to center the movieclip on the page.
Now, in the standalone player, this works. In a browser however, the margins appear to be zero:

var p:PrintJob = new PrintJob();
var startPrint:Boolean = p.start();
printProps.appendText("paper: " + p.paperWidth + "x" + p.paperHeight);
page: " + p.pageWidth + "x" + p.pageHeight);

result in player:

paper: 595x842
page: 559x783

result in browser:

paper: 595x842
page: 595x842

But when printing, the margins are there, and mess up the page layout (not centered + cropping).

Anyone got any idea how to solve this?