Hi maikklein,
you are right, I tried it myself and found the same problem + solution here (you are not alone):
If you already have a Blueprint with parent == your class, new components are added only to the “Defaults”, not to “Components” tab (but can be edited). As as a workaround you can recreate the blueprint and everything is fine. It is a bug and I hope it will be fixed in 4.3 
I filled a bug report: