Setting dateFrom will not display the first day

[StefanGussner]

When setting the dateFrom and dateTo properties the first selected day is not highlighted.
When creating the Element like this:
let ts = document.createElement('range-datepicker');
ts.dateFrom = (1519948800);
// Fri Mar 02 2018
ts.dateTo =1520553600;
// Fri Mar 09 2018
this._list.appendChild(ts);
The first day is not selected.