For the getMonthFullName function the specs state the input should be in the form MM. If call the function with 01 as its input it works fine. I believe php is automatically casting the number to an int and thus removing the 0. However, there are some cases where the function is called
with a variable as input (in my case a get variable) where this casting does not occur. The function then returns nothing. Below is a diff that fixes the getMonthFullName and GetMonthAbbrName for this case.

File bug.php:

<?
require 'Date/Calc.php';
$en_month = Date_Calc::getMonthFullname($month);
echo "Test $en_month";
?>

bug.php?month=01 output:

Before patch:
Test

After patch:
Test January


1434c1434,1436
<
---
>
>       // Cast month to an int to eliminate starting zero
>       $month = (int)$month;
1457a1460
>       $month = (int)$month;