Also there is a horrible bug. IF you create custom task using blueprints, any time you recompile that blueprint it will mess up the instance of that task on any ability timeline that uses it.
The most nasty part however is launching the editor once you add custom bp task, as in ablAbility.cpp : 232 when Able tries to build dependancy list, your blueprint task isn’t initialized yet or something in this line:
if (Task->HasDependencies())
Task is still null so you won’t be able to launch editor.