The DO_ACTION event step allows you to define a sequence of action steps. However in the action editor, any action step with a "wait" property will not be able to be set. Trying to set this property will set it for the DO_ACTION event, not the action step you are trying to edit.

Exiting the action editor after trying to click this checkbox will show that the "wait" property has been wrongly updated for the DO_ACTION event.
Some examples I have observed this with are the action steps SHOW_EFFECT and JUMP.