When a new network adapter is added, Windows tends to put it at the top of its internal adapter list, making it the default for certain functions.
In many cases this is undesired -- unfortunately I'm not aware of any way that the TAP-Win32 driver installer can programmatically override this default.
Luckily, this can be fixed manually by going to Control Panel / Network Connections / Advanced / Advanced Settings. In the top subwindow of the dialog box, move the TAP-Win32 adapter down from the top position.