How to fix custom keyboard layout diacritics dead keys working in very few apps?

I installed the following keyboard layout on Windows:

http://arjenvankol.com/dvorak.php

But the dead keys for the diacritics seem to very rarely work. AFAIK they only work in Word.
When I say it does not work I mean nothing happens when I press the key (followed by another one).

If debugging this is impossible, what would be an easy fix?