Ok this time I think it's a real bug
After some tests, if I make a 'OR' block (Condition A or Condition B)
if Condition A is true and Condition B isn't
And if Condition B is a Sprite condition (like Sprite: [Invert] is visible)
Expression like Sprite.X and Sprite.Y returns 0.
I would expect to get the position of the first instance of the Sprite but it seems, since the condition involving the sprite is false, that c2 can't pick it so it returns nothing as if no sprite were in the layout.
But the thing that is even more weird is that if I use a trigger as Condition A like 'On Start of Layout', the Sprite is properly picked
Anyway, a capx should make more senseor&picking.capx