Oh, thanks Daniel..! I had nightmares of this error, and this js fixed me..!
edit: actually I had to move away from that... (Opted for standard dateinput without calendars:set_value,get_value)
Parsing dates on client side is problematic, since it depends on the users time zone?
Some dates were being read as UTC+2, giving me 29/09/09 22:00 on the server instead of 30/09/09 (inputted value).
And I have users on both sides of the sea...