Start day of calendar trouble

[TRS]

I have a trouble whith the start week day. I changed the ofsset of "calendar.js" to 1 for change the week start on monday and apparently works fine, it shows the numbers of the month starting in monday for every week.

The problem was in the 7 names in the top that indicates the day of week " S M T W T F S", they don't change the order and always start on Saturday.

It seem that the offset only afects the numbered days of the calendar. Do you know because that?
What i need to change moore?
http://lesfarreras.salelles.cat/index.php/reserves

Somebody can help me? Tank you.