I'm currently running V1.25 on ZC 1.3.8a and I'm thinking of upgrading this mod to the latest version 1.10.0. We are on PHP5.2 so that's ok, but will the latest files still work on ZC 1.3.8a?

The reason I'm looking to update to the newest mod version is that I suspect it's the reason why sometimes our customers experience problems with the confirm order button. Sometimes they need to click the confirm order button two or three times before it will actually process. Usually this happens if they've changed the shipping address or added a discount coupon code, or changed shipping methods or anything else that causes the page to propagate with new totals.

Does anyone know if the latest version would cure this issue? Also, is it compatible with 1.3.8a?