Blocks : block:get_movement() returns wrong object type

Sample test (we will push a block named "block" to keep things simple):

block:on_position_changed()
 local dummy=block:get_movement():get_direction4()
end

Effect : [Solarus] [54460] Error: In on_position_changed: scripts/meta/block.lua:2: calling get_direction4 on bad self (movement expected, got movement)