Damn...it's a security problem with the applet. To inject the new pixel format, i have to access a private field. In an application, i can happily set the field to accessible and everything is fine. In an applet, i'm not allowed to do this. It should work if you sign the jpct.jar, if that's an option.
The IPaintListener solution doesn't work, because it never gets called. The AWTGLCanvas calls my paintGL-implementation (where i'm calling the listener's methods) inside paint...but only of the GL context is valid, which it isn't.
Currently, i see two solutions only: Don't use AA or sign the jpct.jar.