Strange slowdown of zlib.

[Magnus Nilsson]

I have the strangest behaviour of zlib on FreeBSD 8.2 (ARM, but I don't
think it's necessarily an ARM specific issue).
Doing
# md5 /lib/libz.so.5
or
# cp /lib/libz.so.5 /tmp/
# export LD_LIBRARY_PATH=/tmp/
slows down applications (I've tested bsdtar and gzip) using zlib to a crawl
on my system.

In the later case, doing
# unset LD_LIBRARY_PATH
reverts the issue.
However, I haven't found any way to recover from the first case, apart from
rebooting - then the execution time is back to normal.

Here is a log of what I describe above (first moving zlib, then doing the
md5):
# cp some2MBfile /tmp/
# time gzip /tmp/some2MBfile
real    0m0.325s
user    0m0.284s
sys     0m0.037s
# rm /tmp/some2MBfile.gz
# cp /lib/libz.so.5 /tmp/
# export LD_LIBRARY_PATH=/tmp/
# cp some2MBfile /tmp/
# time gzip /tmp/some2MBfile
real    0m11.949s
user    0m11.635s
sys     0m0.035s
# rm /tmp/some2MBfile.gz
# unset LD_LIBRARY_PATH
# cp some2MBfile /tmp/
# time gzip /tmp/some2MBfile
real    0m0.325s
user    0m0.288s
sys     0m0.035s
# rm /tmp/some2MBfile.gz
# md5 /lib/libz.so.5
# cp some2MBfile /tmp/
# time gzip /tmp/some2MBfile
real    0m11.919s
user    0m11.608s
sys     0m0.031s
# rm /tmp/some2MBfile.gz

Do you have any idea what could be going on?
Any clues are welcome.

Kind regards/Magnus