Easy to reproduce:

<? get_declared_classes(); ?>

This can be added to, but when it hits that function, boom, sig11.  Note this _only_ happens on ppc linux; there have been no problems on the intel boxes we've tried.

Module list:

xml
standard
session
posix
pcre
mysql
ctype

Other info:
linux 2.2.10-12a, ppc (Yellow Dog Linux)
glibc 2.2.1-0f
gcc version 2.95.3 20010111 (prerelease/franzo/20010111)
apache 1.3.23

Backtrace:
#0  0x100c6b80 in zend_hash_index_update_or_next_insert (ht=0x1016dbe8, h=0, 
    pData=0x7fffe278, nDataSize=4, pDest=0x0, flag=4) at zend_hash.c:375
#1  0x100c4438 in add_next_index_stringl (arg=0x10143800, 
    str=0x1014d9e0 "__PHP_Incomplete_Class", length=22, duplicate=1)
    at zend_API.c:847
#2  0x100cbddc in copy_class_name (ce=0xfdf5604, num_args=0, args=0x7fffe278, 
    hash_key=0x4) at zend_builtin_functions.c:901
#3  0x100c7960 in zend_hash_apply_with_arguments (ht=0x10146b00, 
    destruct=0x100cbd6c <copy_class_name>, num_args=1) at zend_hash.c:731
#4  0x100cbe3c in zif_get_declared_classes (ht=269933544, 
    return_value=0x10173568, this_ptr=0x7fffe278, return_value_used=4)
    at zend_builtin_functions.c:916
#5  0x100e4acc in execute (op_array=0x1016dcf0) at ./zend_execute.c:1598
#6  0x100c1d98 in zend_execute_scripts (type=269933544, retval=0x0, 
    file_count=3) at zend.c:812
#7  0x1001a034 in php_execute_script (primary_file=0x7ffff838) at main.c:1383
#8  0x100174cc in main (argc=2, argv=0x7ffffb14) at cgi_main.c:778
#9  0x0fd94238 in __libc_start_main (argc=2, ubp_av=0x7ffffb14, 
    ubp_ev=0x7fffe278, auxvec=0x7ffffb78, rtld_fini=0x1016dbe8, 
    stinfo=0x100eaba0, stack_on_entry=0x6c657465)
    at ../sysdeps/powerpc/elf/libc-start.c:119