Script to produce the problem:
<?
 
 $TZ=":America/New_York";
 
 $oldTZ = getenv("TZ");
 putenv("TZ=$TZ");
 
 $y = date("Z");
 $x = date("Z");
 
 echo "A: TZ= $TZ: GMTOFFSET = $y <BR>";
 echo "B: TZ= $TZ: GMTOFFSET = $x <BR>";
 putenv("TZ=$oldTZ");
 
 $oldTZ = getenv("TZ");
 putenv("TZ=$TZ");
 
 $y = date("Z");
 $x = date("Z");
 
 echo "A: TZ= $TZ: GMTOFFSET = $y <BR>";
 echo "B: TZ= $TZ: GMTOFFSET = $x <BR>";
 putenv("TZ=$oldTZ");
 
?>

If you swap the lines (at the top of the script):
 $oldTZ = getenv("TZ");
 putenv("TZ=$TZ");
to:
 putenv("TZ=$TZ");
 $oldTZ = getenv("TZ");
the script works fine.

My installation is RH6.2/apache 1.3.12/php4.0.2/mysql 3.22.23.  I also have a 
database logging and replication layer as a module in php, but I had someone
on the PHP GENERAL mailing list verify the bug on their setup.  This appears 
to be a glitch in environment memory handling, but I can't be sure.