mdl-layout__header--scroll not working in small screen

In small screen, the header is no longer scrollable even with mdl-layout__header--scroll. Is it possible enable this in small screen as well? At least tell me how i can achieve this. Thanks

Another simple question, If i add below css modification to mdl layout, will there be any implication? So far it looks fine to me. I need this because i use mdl in concrete5 which has a fixed toolbar on top. Kind of like mdl header. Without this css hack, i would have double scrollbar. The overflow can be any value other than auto or scroll. Please advise. Thanks

.mdl-layout {overflow-y:visible !important; overflow-x:visible !important; }