The bug does not show a compiler error in the blueprint window, no message in the console nor a message in the message log. However, the compile icon does not change to the green arrow indicating a correct compile and when the game is started, a message confirmation shows up that signifies that a blueprint has a compile error.
To reproduce in 4.7.6 in an empty blueprint project without starter-content:
- Create Actor Blueprint named Base
- Create Base Blueprint named Derived (i.e. it is a subclass of the BlueprintGeneratedClass Base)
- In OnBeginPlay of Base add the “Cast To” node for Derived, and connect “Reference to self” to Object.
It can be worked around by not casting to derived classes from a base class and instead expose some function or event that needs to be overriden.