Dead keys are lost in Qt programs

I am not a Qt developer. This bug affects all Qt programs I've used on Windows 7, specifically: Pidgin, VLC, and Texmaker. All of these use the Qt framework (Texmaker uses Qt 4.8 in its current version).

I'm using a UK international keyboard layout where AltGr+: (similarly AltGr+/ and AltGr+) are dead keys. They are used to produce international characters (äöüáéàè...). E.g. to produce ä one would press AltGr+:, then the "a" key. This works fine in every Windows application that does not use Qt. In all Qt applications I've tested, using the dead keys fails most of the time.
If you keep pressing the key combination the special character ("ä") appears about 10% of the time, while 90% of the time the dead key is ignored and the usual character ("a") appears. This is very very very annoying when typing non-English text in applications like Pidgin or Texmaker.

I'll be glad to provide additional info if I can. I've tested this on multiple computers with Windows 7 installed, and it's always only the Qt applications that fail to work with the dead keys.