tilde key doesn't work as deadkey

[robert winter]

Hi,

after I upgraded Ubuntu from 13.10 to 14.04 I can't type letters with a 
makron on top like for instance 'ā' with the 'AltGr' + 'Shift' + '+' - 
shortcut which worked before. Now I get '¯a', so the 4th level on the 
tilde key doesn't work as deadkey any longer. I have no idea how to 
solve this problem.

I use a Dell Inspiron 14 7000 with a German keyboard and German 
settings. I generated a xorg.conf to fiddle with the keyboard options … 
to no avail, so I deleted it again.

Best regards, Robert Winter