Actually, this bug is best described here:

http://superuser.com/questions/801611/how-to-make-all-applications-respect-my-modified-xkb-layout

I'll provide a short summary here too, just in case.

I have a custom layout. Here is a small part of it:

    key <AD02> { [ comma, underscore, Home, Home ] };
    key <AD03> { [ period, ellipsis, Up, Up ] };
    key <AD04> { [ p, P, End, End ] };
    key <AD05> { [ y, Y, Tab, Tab ] };

    key <AC01> { [ a, A, Return, Return ] };
    key <AC02> { [ o, O, Left, Left ] };
    key <AC03> { [ e, E, Down, Down] };
    key <AC04> { [ u, U, Right, Right ] };
    key <AC05> { [ i, I, BackSpace, BackSpace ] };

In other words, you can use Arrows and a bunch of other keys by pressing AltGr + some letter. For example, AltGr+a is Return.

This works across the whole system, it's great. But there are some applications that refuse to respect my xkb layout. Netbeans is one of them.

NetBeans is practically unusable for me. I'm using this layout for so long that switching back to regular keys feels so terrible. Right now I have NetBeans and Emacs (same files opened) side by side so that I can type stuff. It is so painful.

However, it should be noted that this works:

    key <AC07> { [ h, H, question, exclam ] };

In other words, AltGr+h should produce “?”, and it does! Only Arrows, Home, End, Backspace, Return and stuff like that does not work.