MailboxJunkEmailConfiguration reverts to default state

Hello,

On Exchange 2010 SP2 RU6 we are using following cmdlet to edit safe senders list, it works well but after a while users' safe sender lists are reverting to previous state.

get-Mailbox | Set-MailboxJunkEmailConfiguration -TrustedSendersAndDomains @{Add='address@domain1.com','domain2.com'}

Do you have any idea about this issue?

Thanks