I have the same bug.
This function is OK with Powershell ISE, but doesn’t work with PowerGUI
Start-Process -FilePath "C:\WINDOWS\System32\cmd.exe" -Credential $credential -ArgumentList ("/c $sFileExecutable")
It works with the WorkingDirectory
parameter
Start-Process -FilePath 'cmd.exe' -Credential $credential -ArgumentList ("/c $sFileExecutable") -WorkingDirectory 'C:\Windows\System32'