Excluded list of Domain Controllers

I'm trying to set the excluded list for DCs on an Exchange server. However using

Set-ExchangeServer exch2k10.domain.local -StaticExcludedDomainControllers dc2.domain.local -DomainController dc1.domain.local

doesn't seem to be modifying anything, because querying back using

Get-ExchangeServer exch2k10.domain.local -DomainController dc1.domain.local | fl StaticExcludedDomainControllers

shows an empty list.

What could be wrong ?