Assume that you set values of calendar processing parameters (such as the ConflictPercentageAllowed and MaximumConflictInstances parameters) to 0 to forbid any conflict for recurring meetings in a Microsoft Exchange Server 2013 environment. When you book two adjacent recurring meetings that have a start date six months ago from now on the same room mailbox and then you make their running time conflicted, these bookings are not declined.
This issue occurs because conflicts for recurring meetings are only checked for the latest six months.
To resolve this issue, install Cumulative Update 9 for Exchange Server 2013.
To work around this issue, delete the old recurring meeting, and then create a new one that recurs from today to the end date.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.