KDE, Cinammon, Gnome-Shell, LightDM. It quite complicated set of software.
I think the problem lies in Arch's KISS philosophy which forbids any additional configuration. If you sacrificed some of your time to polish the configuration, you probably wouldn't have this kind of problems. On Fedora I also have some bugs (about 5 of them), but all of them are small fries. Do you really want to work on Arch? I think you would be better off with a distribution which is less "do-it-yourself". The thing is, with added complexity of modern software much more combinations of configuration are possible, which leads to many more conflicts and the defaults are less likely to be the right settings.