I've found a reason of this issue. Month view was created using server time (respecting time zone) mixed with EPESI regional time (set by user). First day of month(rather it's unix timestamp) was obtained properly, but first day to display(unix timestamp too) from previous month was wrongly calculated, so all days were shifted by one. You can reproduce this issue, when you set your EPESI time zone to the east of your server time zone. Your server time zone is America/New York which is GMT-6, but your EPESI time zone was GMT+1, so calendar was screwed up. When I've changed EPESI timezone to GMT-6, then month view was generated properly.
I've fixed this issue. It will be included in future release, but if you want to fix your installation now, please use attached fix.
Thanks for your test installation, that helped me a lot to find this issue!