Magento Onepage Checkout Template Bug

Recently, we rolled out an installation of Magento 1.3.2.3 for one of our clients but ran into small a problem along the way. Being an established open source project, I initially assumed that the error was my own when I found that the onepage checkout process would stop working half way through (step 3 to be exact).  However, after digging around, I found that the problem was actually a bug in Magento’s JavaScript.  The bug has been reported and will hopefully be fixed soon, but in the meantime, here’s the fix and how I found it. …