The thing is that some of the templates do not support head banner uploading feature. In version 4.0.0 buttons for such templates were not grayed out but during uploading procedure there was error message which indicated that template does not support this functionality. In current 4.1 version buttons for such templates are disabled. Indeed, most of the templates do support this feature. In the attachment you can find banner_list.txt file which contains the list of templates which support banner uploading feature. This list was made on clean 4.1 installation.