Powershell custom action not working

I am using InstallShield 2012 Spring.

I am trying to run a Powershell custom action on Windows Server 2012. I am able to run the Powershell script from the ISE and it all works correctly. However, when I attempt to call a Powershell custom action from my install, the custom action runs but doesn't work.

I have set IS_PS_EXECUTIONPOLICY = Bypass in the property manager.

The first part of my Powershell script is shown below:

Install-WindowsFeature Web-Filtering > $env:temp\InstWin2k12Features.log
Install-WindowsFeature Web-ISAPI-Filter >> $env:temp\InstWin2k12Features.log
Install-WindowsFeature Web-ISAPI-Ext >> $env:temp\InstWin2k12Features.log

The rest of the lines of my script are just installing different features and appending the results to the same log file. The Powershell custom action is sequenced as a Deferred Execution in System Context custom action.

I installed 2012 Spring SP1 and that hasn't changed anything.

Does anybody know what might be wrong?