sprintf() oddity

["Chris Boget" <chris.boget@xxxxxxxx>]

What's going on here:
 
$number = 5000000000.1234567890;
echo sprintf( '%.05f', $number );

result: 5000000000.12346
 
$number = 5000000000000.1234567890;
echo sprintf( '%.05f', $number );

result: 5000000000000.12305
 
$number = 5000000000000000.1234567890;
echo sprintf( '%.05f', $number );

result: 5000000000000000.00000
 
Why isn't it formatting the decimals properly? And apparently losing
some?
 
Running PHP 4.3.11 on Windows Server 2003 box.
 
thnx,
Chris