One thing you may want to consider - I have been having some problems of my own with mod_perl resulting in my system running out of threads. This has forced me into researching threads in much more depth. One thing I have seen multiple times is that localtime() is not thread safe. While this doesn't seem to explain my issues it might explain yours. You can set the environment all you want, but if another thread comes along the TZ can get set to something else, even while localtime() is running, unless you have done something to lock access during your critical time between setting the TZ and getting a result from localtime().