[Orgmode] Org-mode completely freezes emacs

[Simon Winwood]

       When using org-mode, occasionally (semi-unrepeatable :( emacs
locks up completely: 100% CPU, doesn't respond to C-g, does respond to
X-redisplay requests --- a kill is required.  

        Unfortunately, the bug isn't readily reproducible, although it
happens reasonably frequently.  It sounds more like an emacs bug, but
it seems to occur only in org mode.  

        Any ideas?  It might be a font-lock bug, but without being
able to reproduce the bug, I can't really tell.

     Thanks,

        Simon

Versions:
Linux Ubuntu (Edgy)
Emacs 22.0.50-1 (emacs-snapshot-gtk in Ubuntu)
Org   4.44

A GDB attach and backtrace gives (although I don't know how much I
trust it):

0x08197806 in matherr ()
(gdb) bt
#0  0x08197806 in matherr ()
#1  0x08197930 in matherr ()
#2  0x08198864 in matherr ()
#3  0x08198b9e in matherr ()
#4  0x08135c6c in abort ()
#5  0x0815a705 in re_compile_pattern ()
#6  0x0818523d in matherr ()
#7  0x0815a11a in re_compile_pattern ()
#8  0x0815a542 in re_compile_pattern ()
#9  0x0818523d in matherr ()
#10 0x0815a11a in re_compile_pattern ()
#11 0x0815a542 in re_compile_pattern ()
#12 0x0818523d in matherr ()
#13 0x0815a11a in re_compile_pattern ()
#14 0x0815a542 in re_compile_pattern ()
#15 0x0818523d in matherr ()
#16 0x0815a11a in re_compile_pattern ()
#17 0x0815a542 in re_compile_pattern ()
#18 0x0815bbb1 in error ()
#19 0x0815bd3f in error ()
#20 0x0815a87a in re_compile_pattern ()
#21 0x0815ba39 in error ()
#22 0x080f7625 in abort ()
#23 0x08159142 in re_compile_pattern ()
#24 0x080fce17 in abort ()
#25 0x08103350 in abort ()
#26 0x08159142 in re_compile_pattern ()
#27 0x080fcec3 in abort ()
#28 0x081591fa in re_compile_pattern ()
#29 0x080fd93c in abort ()
#30 0x080fdcfa in abort ()
#31 0x080fdde7 in abort ()
#32 0x080f3c65 in abort ()
#33 0xb75888cc in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6