I'm at a loss to explain what might be going on. Typically......
The same username and password, means the same user profile would be used, which of course includes your "desktop" settings.
The only thing I can think of is that perhaps someone has configured a login script that is running at startup that samples a condition (maybe the network addressing schema) and based on that script it calls the default user profile or another profile to be used under certain conditions.
I know back in the day we used to set "mandatory" (roaming user profiles) but they were based on Group Policy in an Active Directory Domain, which is not to say that Group Policy isn't involved, I'm just not sure what configuration might be used.
I haven't played with roaming user profiles or GPOs since back in Server 2k3 days. I'm sure features and functionality is much more robust now. Heck there might even be one based on "location".