When Right key is released, the animation should be set to Right Sprite AND must stop. It's OK.
When Right key is pressed, the animation should be set to Right Sprite AND must start. Unfortunately, the animation loops only once, even with the Loop property set to Yes.
The same occurs for the other 3 sides (up, left and down). It's a 8-movement object, with 4 directions.
I use Win XP and the latest versions of Firefox and Chrome. And I have the new Construct 2 R55. Best.