In fact, it is another day is checked as well, so I can sure that it isn't the behavior you are seeing.
And if none of other days is checked, it is impossible to uncheck the "last".
The issue is:
It is more than one day is checked(include last), and I just uncheck the "last" and then click OK, the UI looks everything is work well and it is not any error or exception showed. But unfortunately, when I reopen the trigger, the "last" is still checked.
And I check it with "task scheduler" in windows as well, and I think maybe there is a mistake to assign true to "RunOnLastDayOfMonth" property in MonthlyTrigger when click the "OK" button.
And if none of other days is checked, it is impossible to uncheck the "last".
The issue is:
It is more than one day is checked(include last), and I just uncheck the "last" and then click OK, the UI looks everything is work well and it is not any error or exception showed. But unfortunately, when I reopen the trigger, the "last" is still checked.
And I check it with "task scheduler" in windows as well, and I think maybe there is a mistake to assign true to "RunOnLastDayOfMonth" property in MonthlyTrigger when click the "OK" button.