We're on a heavily modified EE 22.214.171.124 with some 20 store views - some of them sharing the same language - facing a problem with url keys.
These are generated and differ per language BUT this doesn'...
I have Authorize.net Direct Post enabled on Magento 1.13 with the following settings:
Payment Action: Authorize Only
Test Mode: No
Gateway URL: https://test.authorize.net/gateway/transact.dll