Data taken from another day besides the specified interval

Hey, I am using the piwik 1.6 API, the method Live.GetLastVisitsDetails, and I have to search for data using the period=‘range’ and date=‘start-date,end-date’. This thing also retrieves me some data below the start-date date, more precise some data from ‘start-date - 1’, just some data not all of it.

Do you have any idea why this happens?

Thank you,

Crisan Tudor