From Bug #13900
date("I") does not identify if a date occurs during daylight saving time correctly.

[2001-11-06 00:20:42] jimw@php.net

if you want to check if a date occurs during daylight savings time, you have to set your
timezone to one that observes daylight savings time. (ie.
putenv("TZ=PST8PDT"))

there's no bug here.

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There may not be a bug but there is a issue here.  What about timezones that don't observe daylight saving time (Like the entire state of Arizona)?  Are the millions of us that fall under that category just out of luck?

By the way, Arizona is the home of the World Series Champion Diamondbacks!