Automatic push profile distribution not working

Using Profile Manager I've been able to enrol numerous devices to our Mac server and configure them on our .private network. Earlier today I made some changes to one of the Settings profiles, enabling a custom wallpaper I designed. From tinkering with Server I noticed profile updates (to System Prefs etc.) seem to update on first boot of a Mac or user login. I was left scratching my head when the wallpaper I added either failed to load, appeared on login but then disappeared again after logging out. All my profiles in System Prefs, apart from this one, are verified. This one is unsigned. My first question, would this be the reason my wallpaper isn't staying where it's supposed to? I decided to manually re-add my 'suite settings' profile and everything changed. All dock items appeared as desired and wallpaper stayed in the background. Ideally I'd like things like this to change automatically instead of me going round every machine.

Does anyone know why automatic push distribution isn't working as it's supposed to? It's enabled within Profile Manager and I can see the changes sit in 'Active tasks' before appearing in 'Completed tasks'. Perhaps a few more ports need unblocked? Or maybe I've locked the settings down too much? Any ideas?

Thanks! Chris