It works with "every 4 seconds" choice, but not with "trigger once" (in this case all got unamovible). Thanks LittleStain.
Your opinion OddConfection was brilliant and simple too. But, is there a plus with the stopped flashing when the SpriteA is not moving anymore?
Anyway, thanks for your assistant, dudes.
EDIT: I can answer myself XD. Only decrease the interval of flashing at minimum value and it stops almost at same time that sprite stops its movement. Isn't it?