1.- put the two keyboard events at root (not inside System Layerangle rot angle)
2.- Make the +45 angle activate group "ROTATE 45 RIGHT"
3.- Inside the group on a blank event put the action "add +45 to sprite"
4.- Inside the group on a second blank event put action: Deactivate "ROTATE 45 RIGHT" group.
do the same for rotate -45
hope that helps