@Aron Prins: If you are having problems with the Domain Mapping plugin, it has to be installed properly, and configured in a very specific way. I have detailed Domain Mapping instructions.
I have Not noticed any problems with WP version 4.2. If you have changed versions of the plugin, you may need to force updating the settings, there are different options on different versions of the plugin; uncheck something and save, then set each option how you want, to force updating the settings.