Dynamic Distribution groups via powershell

hi

i have created a DDG through powershell which checks against the Users AD attributes - Office and Mobile Phone.

Set-DynamicDistributionGroup "hasmobile" -RecipientFilter {(RecipientType -eq "UserMailBox") -and (MobilePhone -ne $Null) -and (Office -eq "ABC")}
$tmp = Get-DynamicDistributionGroup "hasmobile"
get-recipient -RecipientPreviewFilter $tmp.RecipientFilter

This works as expected in Powershell and changes to the AD object  stop it being returned . e.g. removing/adding a mobile number

I have then created a mail flow rule to apply when "if the sender is a member of this group" = "hasmobile"

However, when i run this it always applies this rule regardless of whether the rule is matched or not.

I have also tried appending a

"-RecipientContainer 'DC=ABC,DC=local'"

to the filter via powershell but this still does not work.

Can anyone elaborate on why this is getting applied when the criteria does not match please ?

any help greatly appreciated.