Cannot add WFE to new Patched Farm (June 2012 CU)

I cannot add a WFE to my new, patched, farm.

The App Server/Farm is at build 14.0.6123.5000 (SP1+June CU) and the WFE is reported as 10.0.6029.1000 (I installed the June CU, but it doesn't seem to have registered). 

When I attempt to add the WFE to the Farm, the WFE complains that it's missing features from the App Server build 14.0.6120.5000. How is this possible?

I note that some of these components it's complaining about, e.g. Visio Services (KB 2598354) aren't installed on my App Server, but surely this isn't required if the server itself is patched?