This post discuss a specific issue that may occur during mailbox moves in complex environments with multiple Active Directory Sites and multiple Exchange servers. There are several other settings which must be in place in order for this issue to present itself. First, here are the settings which need to be in place:
1. On both the Source and Target mailbox stores, set Deleted Mailbox Retention to 0 days.
2. Note what the Online Maintenance schedule is set to on both stores. The moves need to be scheduled to coincide with Online Maintenance on the Target mailbox store.[…]