Problem Move New User on Powershell

Hi, i have big problem.
I created 2 users login, lpereira and alessandram but i need to move lpereira_prest and alessandram_prest to lpereira and alessandram.

When i use

$user = Get-SPUser -web http://rj2k8shp01 -Identity "DOMAIN\XXXXXXXXX_prest"

Move-SPUser -IgnoreSID -Identity $user -NewAlias "DOMAIN\XXXXXXXXX"

The operation was successfully but when i try get user again obtain

I tried this operation with other users and operation is successfully.

Where's the problem ?