A small update on the matter.
First of all, there's a major bug/problem in php 5.4 (php 5.3.8 I also tested it on is not affected). The short version of month names in Czech locale is incorrect and it's set to a number of the month (so February is 2, etc.). This causes the formats with short month name to fail when the selected language is Czech. It's not something we can really fix.
Another problem is, there is also a small bug in EPESI that this issue makes apparent. And due to that error, EPESI processes dates incorrectly regardless which language is selected.
We'll include a fix for the latter issue in release 1.4.1 that we're hoping to have ready within this week.
Kind regards,
Arek