We have found that if your Week View component starts from a Sunday and you put an event in the Sunday, Monday will display a full day too.
Additionally, if the Sunday event extends to 24:00, then a full day is displayed on the Tuesday.
It seems to only happen on this week, every year.
I believe this is a known bug, and something on our backlog to fix. You can get in touch with support to confirm, which will somewhat help us up the priority.