Windows PowerShell script issue/AD issue

Hi,

We are running a powershell script to fill in some AD attributes and its a pretty standard script:

import-module ActiveDirectory
Set-ADuser -Identity "User1" -Department "Department1" -title "Title1" -replace @{extensionAttribute10="01/01/2001";extensionAttribute11="August 20"}

Now my problem:
When we run this script everything seems to be working fine.
Only after 24h the Title field in AD is cleared out, the department field and the extension attribute are still filled with the info.

Any thought on why the Title field keeps clearing after 24h?
When filling in the Title field manually it works fine.

Thanks in advance.