I'm not sure exactly, but is it possible that this is the result of a configuration setting in .NET? There might be a master date format that was configured when .NET was installed. At the time (no pun intended) the server was configured with the undesirable datetime format. Despite changing the server setting, the format remains the same because of the .NET configuration. I could be completely wrong of course.
You might start by comparing the framework config files between your two servers.