All right, my bad, my assumption was incorrect indeed.
Still, the fact is that during the 2 seconds of wait, actions are memorized and then duplicated.
Strange thing is I tried to add a "Trigger once while true" condition to the "Is on-screen" condition, and then nothing at all happens. That was quite unexpected.
Anyway, after having tried a bit a bit I came up with a solution.
Simply place the "destroy red ball" action before the wait one.
Then the red ball is destroyed, and two seconds later, 4 blue balls are spawned.
But that's probably not what you want. I guess you want the ball to run it's course, then explode (spawn blue balls).
The bug you are relating to appears to be a physics bug.
Line 225 in Physics_behavior.js (right in the minified section) : a is null
Apparently, this is the red_ball physics in cause, since the object was destroyed, but still trying to apply some function to it.
Remove the physic behaviour to the object, you will just have a lot of spawns but no crash.
For ashley : reproduction of the crashing capx
Sprite = explode_ball; Sprite2 = blue_ball
As stated above, placing the "destroy Sprite" action first, works. Spawning of Sprite2 occurs after 2 seconds, on the former position of the Sprite object.
Adding a "Trigger once while true" don't seem to work.