I've looked further into this and made a fix in the current Development Version.
I'd appreciate it if you could test this version out and if it appears stable, I'll publish it to 1.0.14.
Some info in case someone's googling WordPress timezone problems:
WordPress allows you to set your timezone in admin settings (the WP option is called 'timezone_string'), but PHP knows nothing about this unless it is passed to the native
WordPress kindly does this on the admin screen where you set the timezone option, but this won't persist and nowhere else in the system does this get set. The rest of the time your system is forced into UTC and WordPress tries to handle things itself. However, if you try to format a date with a timezone, all WP does is tack the offset onto the end of the date, creating an incorrect date.