Joining a minecraft server which has a tab header/footer if you leave that minecraft server and goto another server without a header/footer, You see the header/footer from the previous server on the server you are currently on.

Explained:
Join server #1, Make sure server #1 has a tab header/footer
Now leave server #1 and head to server #2, Make sure server #2 does NOT Have a tab header/footer, If you press tab you should now see the tab header/footer from server #1

I also would like to point out, Even if you join a server with a tab footer/header and don't open the tab on there, You will still see that servers tab header/footer on another server without one..