STATUS
Defect ID MMEX-2546 is acknowledged . A Hotfix is scheduled for the End of June 2017 (edit - now available at https://support.quest.com/migration-manager-for-ad/kb/77417).
WORKAROUND
1) Create a Public Folder mailbox in o365 or the On Premises exchange server (the mailbox itself can be empty).
2) Wait a small period of time for target user properties to update
3) Allow the MaGE agent to sync the mailbox which will update the targetPublicFolderEmailAddress value
4) Re-try the switch operation
