Stuck kernel while cleaning up the object tree

Hello,

On recent -current machines, I have seen a common pattern, with the machine 
being frozen (still responsive to pings, though) in the initial phases of the 
buildworld procedure :

example freeze :
--------------------------------------------------------------
>>> stage 2.1: cleaning up the object tree
--------------------------------------------------------------
cd /usr/src; MAKEOBJDIRPREFIX=/usr/obj  MACHINE_ARCH=i386  MACHINE=i386  
CPUTYPE=  GROFF_BIN_PATH=/usr/obj/usr/src/tmp/legacy/usr/bin  
GROFF_FONT_PATH=/usr/obj/usr/src/tmp/legacy/usr/share/groff_font  
GROFF_TMAC_PATH=/usr/obj/usr/src/tmp/legacy/usr/share/tmac  
_SHLIBDIRPREFIX=/usr/obj/usr/src/tmp  VERSION="FreeBSD 8.0-CURRENT i386 
800074"  INSTALL="sh /usr/src/tools/install.sh"  
PATH=/usr/obj/usr/src/tmp/legacy/usr/sbin:/usr/obj/usr/src/tmp/legacy/usr/bin:/usr/obj/usr/src/tmp/legacy/usr/games:/usr/obj/usr/src/tmp/usr/sbin:/usr/obj/usr/src/tmp/usr/bin:/usr/obj/usr/src/tmp/usr/games:/sbin:/bin:/usr/sbin:/usr/bin 
NO_CTF=1 make -f Makefile.inc1 DESTDIR=/usr/obj/usr/src/tmp par-cleandir
===> share/info (cleandir)
===> lib (cleandir)
===> lib/csu/i386-elf (cleandir)
[type ^T in the console]
load: 0.00  cmd: sh 24587 [*Name Cache] 0.01u 0.00s 0% 1584k

The other machines also froze while "cleaning up the object tree".

The machines are configured with serial consoles : I have no kernel stack 
backtrace to aid in pinpointing the cause of this freeze.

	Cheers

	TfH