Variable Definitions Breaking Child Objects?

Very weird issue. I have a parent object named par_organism and three children, obj_drone, obj_soldier, and obj_queen. All the variables in these objects are exactly the same and no custom events. Some variables are defined in Variable Definitions and some are defined in the create event, but the ONLY variable that is different in soldiers vs drones & queens is that the soldiers have the stance variable in the Variable Definitions set to "Attack" by default and the parent object is set to "Flee" by default. However, by changing this one variable, obj_soldier would no longer run the Step event. Nothing else changed.

I set the stance variable back to "Flee" and then SET IT BACK to "Attack" and it started working again! What the actual F***!? Anyone else encounter weird bugs like this? Is there something about variable definitions I don't understand? Should I not be using them with parents? I'm so scared that bugs like this will carry over into my published game...