High Availability - Same version, different build/patch level

Hi. We are patching our SQL Servers in 2014, i.e. Service packs. We have 3 nodes in High Availability. My understanding is that you can't have different versions in the same availability group (i.e. 2014/2012). But are there any issues with having servers in the same Availability Group that are on different Service Packs or cumulative update (CU) build levels?