Input of non-ASCII characters not working anymore

I am not able to input non-ASCII characters like é,è,ô,ü etc anymore. I am using an US keyboard layout and am composing my accented characters with it.

[Alt Gr] I + I gives me î for example, same for the other letters.

If i switch layout, lets say to French, these characters can be inputed with no problem.

What stopped working is the ability to compose characters which juste gives the squared question mark character now.

Qt 4 and GTK don't show this issue on the same system.