Get-MailboxStatistic returns wrong data

All! I have Exchange 2013 organization: several exchange servers, multiple mailbox database. To defragment on of the MDB1 (want to reduce size), i've created new MBD2 and move all maboxes from MDB1 to MDB2 with command

Get-Mailbox -Database MDB1 | New-MoveRequest -TargetDatabase MDB2

After all moverequests are completed i check MDB1 with command

Get-Mailbox -Database 'MDB1'
Get-Mailbox -Database 'MDB1' -PublicFolder
Get-Mailbox -Database 'MDB1' -Monitoring
Get-Mailbox -Database 'MDB1' -Arbitration

and gets only one monitoring mailbox.

But if i run command

Get-MailboxStatistics -Database 'MDB1'

i get about 40 mailboxes and disconnectreason for this mailboxes is empty (all softdeleted mailbox a've removed with command remove-storemailbox).

Ok, lets ckeck some of this mailboxes individually. For example:

Get-MailboxStatistics 'John Smith'

show me that this mailbox is placed in... not in MDB1, but in MDB3! And allother mailboxes do so

So, my question is: why Get-MailboxStatistics with 'Database' parameter show wrong data for mailboxes? Why this command show wrong database?

By default, the Get-MailboxStatistics cmdlet would return all mailboxes regardless of it's active, softdeleted or disabled.

How did you confirm that "disconnectreason for this mailboxes is empty"? Were these mailboxes moved from MDB1 to MDB3? If yes, it could be due to that Exchange would keep a "soft copy" of mailboxes on the source database that are moved to another database until the retention period is up.

Run the command below instead and see if these mailboxes would be returned:

Get-MailboxStatistics -database MDB1 | Where {$_.DisconnectDate -eq $null}