TUI-Calendar: Different End-date while dragging or typing in the dates

I'm trying to get the TUI-Calendar running but,

when I'm dragging an event over days it correctly gives me the start- and end date. But if I type in the dates it gives me the correct start date but the end date -1 day.

My question is where can I find the different handlers for the "drag and drop" and "typing in" version of creating an event, so that I can code a workaround.