Problem with booking


Could you please look at my site : and try to book 21 Grudzien 2012 (21'th December) 12:00 pm. As you can see the slot of time is green(free, "termin wolny"). This time slot has been booked and confirmed previously. If you try to confirm this appointment( "kliknij w celu potwierdzenia wizyty"), you'll receive alert that this slot time is busy ("Przepraszam..."). Why this time slot hasn't been filled with correct color previously(busy was customized as red like in legend) ?

Tested with Chrome, Mozilla, IE 8. Wordpress 3.4.2.
Regards ,