EVALUATION

It is possible to not include MwmUtils.h header altogether. Motif will be phased out in jdk7 and is not supported in openjdk anyway; XAWT-related code depends on presumed structure fields size  elsewhere. Actually if one does create a native application setting for instance these hints via XChangeProperty, resulting hints will be different for Motif/Openmotif and Lesstif sets of headers.
I propose explicit declaration of the structure in the only place it is used in XAWT.
                                     

EVALUATION

After a long discussion, it has occured the problem is with some incompatibility between openmotif and lesstif. Their 32bit code is very close to each other, while in 64bits some structures (like PropMwmHints) has different sizes, which causes so strange problems.
                                     

EVALUATION

Not reproducible with JDK7.0-b16 on linux-amd64 with GNOME 2.8. Need more information about the environment where this bug can be reproduced.

The sample application used to reproduce this issue is as follows:

import java.awt.*;

public class frame {
    public static void main(String[] args) {
        Frame f = new Frame("My Frame");
        f.setBounds(50, 50, 200, 100);
        f.setVisible(true);
    }
}