Simple GLX test program crashes

Here's a simple program that crashes on my Ubuntu 7.04[1] - compile and run with "gcc -Wall -g test.c -lX11 -lGL && ./a.out".
GDB tells me it crashes in the second glXQueryVersion[2]. Removing the first XCloseDisplay "fixes" the crash, indicating that GLX gets confused when a second Display is opened at the same address as the first. OpenGL is working fine for me doing much more complicated things (games), so this seems like a simple overlooked case in the GLX core or in the radeon driver.

Relevant configuration is:
Ubuntu 7.04
Pentium M 1700 Mhz
Radeon 9700 mobile
I'm using the "radeon" open source driver, _not_ the ATI provided fglrx driver.

Excerpts from glxinfo:
direct rendering: Yes
OpenGL vendor string: Tungsten Graphics, Inc.
OpenGL renderer string: Mesa DRI R300 20060815 AGP 4x x86/MMX/SSE2 TCL
OpenGL version string: 1.3 Mesa 6.5.2

[1]
#include <X11/X.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <GL/glx.h>
#include <stdio.h>

int main(int nargs, char **vargs) {
    int major, minor;
    Display *disp = XOpenDisplay(NULL);
    glXQueryVersion(disp, &major, &minor);
    fprintf(stderr, "%p: %d.%d\n", disp, major, minor);
    XCloseDisplay(disp);
    disp = XOpenDisplay(NULL);
    glXQueryVersion(disp, &major, &minor);
    fprintf(stderr, "%p: %d.%d\n", disp, major, minor);
    XCloseDisplay(disp);
    return 0;
}

[2]:
elias@elias-laptop:~/glxcrash$ gdb ./a.out
GNU gdb 6.6-debian
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This GDB was configured as "i486-linux-gnu"...
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
(gdb) run
Starting program: /media/hda6/storage/glxcrash/a.out
[Thread debugging using libthread_db enabled]
[New Thread -1212192560 (LWP 19851)]
0x804a008: 1.2

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1212192560 (LWP 19851)]
0xb7a11940 in ?? ()
(gdb) bt
#0 0xb7a11940 in ?? ()
#1 0xb7dc1ab1 in __glXInitialize () from /usr/lib/libGL.so.1
#2 0xb7dbda1d in glXQueryVersion () from /usr/lib/libGL.so.1
#3 0x080485db in main () at test.c:14