BlockTime off by one month

I don’t understand why this

sBlockTime = { 
			start_date: new Date(2013,1,13,13,0,0,0),
			end_date: new Date(2013,1,13,16,0,0,0),
			css:   "BlockTime",
			type:  "dhx_time_block", 
			sections: { timeline: 1, unit:1} 
		if (sBlockTime) scheduler.addMarkedTimespan(sBlockTime);

displays as blocked time for the month of February, and not January. Is this a bug or expected behavior?

When you creating Date by js Date constructor, beware that months are zero based, so 1 is February