Multi-threaded UI Freezes on GDK Call

[Michael McCann <naetrick comcast net>]

I've got a multithreaded GTK application. One thread runs gtk_main():

gtk_threads_enter();
gtk_main();
gtk_threads_leave();

The other thread is an infinite loop that sleeps for one second on each 
loop. Every x seconds, the infinite loop calls a function, which makes 
some GDK calls. At the beginning of this function, gdk_threads_enter() 
is called; at the end, gdk_flush() and gdk_threads_leave() is called.

Whenever this function is called, the UI freezes and CPU usage jumps to 
100% for about one second (no other applications freeze, of course). 
I've tried calling gdk_threads_leave()/enter() before and after each GDK 
call to no avail. I run g_thread_init() and gdk_threads_init() at the 
beginning of my program.

In the function, gdk_screen_get_default(), gdk_screen_get_root_window(), 
gdk_pixbuf_get_from_drawable(), and gdk_pixbuf_save_to_bufferv() are 
called.

I'm using NetBSD on a P4 1.2GHz. What am I doing wrong? I've asked this 
question on IRC (irc.gnome.org, #gtk+) but noone seems to know the problem.