This bug has been reported on the Debian BTS 2 months ago by Michael Musenbrock. It is easy to reproduce with 6.5.2 (and Xserver 1.3-rc3). Just start the game (trackballs) and press "new game" and then "start game".

I got the following backtrace with mesa 6.5.2:

$ gdb trackballs
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This GDB was configured as "i486-linux-gnu"...(no debugging symbols found)
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".

(gdb) r
Starting program: /usr/games/trackballs 
(no debugging symbols found)
[...]
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1218623808 (LWP 5830)]
0xb71e5b64 in _save_upgrade_vertex (ctx=0x8155098, attr=2, newsz=3) at tnl/t_save_api.c:406
406	tnl/t_save_api.c: No such file or directory.
	in tnl/t_save_api.c
(gdb) bt full
#0  0xb71e5b64 in _save_upgrade_vertex (ctx=0x8155098, attr=2, newsz=3) at tnl/t_save_api.c:406
	tnl = (TNLcontext *) 0x8396d70
	oldsz = 0
	i = <value optimized out>
	tmp = <value optimized out>
	__PRETTY_FUNCTION__ = "_save_upgrade_vertex"
#1  0xb71e66aa in do_choose (attr=2, sz=3, attr_func=0xb71e41b0 <save_attrib_2_3>, choose1=0xb71e77f0 <save_choose_2_1>, choose2=0xb71e77a0 <save_choose_2_2>, choose3=0xb71e7750 <save_choose_2_3>, 
    choose4=0xb71e7700 <save_choose_2_4>, v=0xbfc9c91c) at tnl/t_save_api.c:561
	ctx = (GLcontext *) 0x839a000
	tnl = (TNLcontext *) 0x8396d70
	i = <value optimized out>
	id = {0, 0, 0, 1}
#2  0xb71e7793 in save_choose_2_3 (v=0xbfc9c91c) at tnl/t_save_api.c:665
No locals.
#3  0xb71e30f3 in _save_Normal3f (x=0, y=0, z=1) at tnl/t_save_api.c:840
	v = {0, 0, 1}
#4  0xb727ee9c in loopback_Normal3dv (v=0xbfc9ca70) at main/api_loopback.c:387
No locals.
#5  0x08056bd2 in ?? ()
No symbol table info available.
#6  0x08057af4 in ?? ()
No symbol table info available.
#7  0x0804e7e7 in ?? ()
No symbol table info available.
#8  0x0804cc49 in ?? ()
No symbol table info available.
#9  0xb7e9a5d2 in scm_boot_guile () from /usr/lib/libguile.so.12
No symbol table info available.
#10 0x0804beca in ?? ()
No symbol table info available.
#11 0xb79a8ea8 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
No symbol table info available.
#12 0x0804bc61 in ?? ()
No symbol table info available.