Update: See my second reply below.

Old Update: This is a bug in old versions of the POSIX module: see here, for example. I see this bug with Perl 5.8.0, but not with 5.8.6. (I don't know exactly which version fixed it.) Is upgrading an option for you? If not, you might have to use one of those other modules after all...

PPS. Looks like downgrading would also fix it: it's working properly in 5.6.2.

PPPS. But don't upgrade too much! I get the bug again with 5.8.7. This is very odd. Maybe it's affected by the build options or something, but I can't see an obvious pattern.

I can only offer the faintly unhelpful "it works for me": with your code I get:

Tue Nov  1 17:16:55 2005 Tue 01 Nov 2005 17:16:55 CST
Tue Nov  1 18:16:55 2005 Tue 01 Nov 2005 18:16:55 EST
[download]

  env TZ=America/New_York date
  env TZ=America/Chicago date
[download]

Also, do you get the correct offset if you add %z to your strftime format?