Month doesn't change, and today button breaks, on 1st of month in month view
If the current day is selected in month view in month N, when Calendar rolls over to the first of month N+1, it doesn't switch to displaying the new month. This is presumably because the 1st of month N+1 is displayed as a greyed, empty tile in month N (except if it falls a Monday).
Additionally, in this situation, the Today button does nothing to change to month N+1 or focus the current day in this situation, again presumably because the greyed/empty tile for the 1st of month N+1 from the month N view is selected. Selecting another day in month N and then clicking Today successfully changes the view to month N+1.
This may also affect other beginning-of-month-N+1 days that are displayed as greyed tiles in month N, but II haven't tested this.