text get cropped in the image

I don't know what is causing this...
but after a while, maybe upgrading php and the gd library ( now there's php > 5.2 on the server) some images created by signwriters cut the text vertically.
This happens when i have some higher glyphes compared to the normal ones, but the weird thing is that it didn't happen from the beginning..
any idea?
Thanks,
Da.

This is the code i use, anyway...

$titolo->fontfile = 'ampersand.ttf';
$titolo->fontsize = 21;
$titolo->foreground = 'b7000f';
$titolo->background = 'ffffff';
$titolo->maxwidth = 710;
$titolo->transparent = true;
$titolo->textalign = right;