Cannot delegate access to all mailboxes in database by powershell

Halo

I can give any access right to mailboxes whether by powershell ( Get-mailbox | Add-ADPermission) or EMC

But setting rights on maildatabase level doesn't apply to mailboxes

[PS] C:\Windows\system32>Get-Mailboxdatabase testdb | Get-ADPermission -User testadmt | fl user,accessrights,ExtendedRights,*inher*

User                : ICATON\testadmt
AccessRights        : {ExtendedRight}
ExtendedRights      : {Receive-As}
InheritedObjectType : ms-Exch-Private-MDB
InheritanceType     : Descendents
IsInherited         : False

[PS] C:\Windows\system32>Get-Mailbox svistunova | Get-ADPermission -User testadmt | fl user,accessrights,ExtendedRights,
*inher*

[PS] C:\Windows\system32>Get-Mailbox svistunova | fl *database*

Database                     : TestDB