It looks like it's got to do with the collision cells.
The layout is effectively split in to cells the size of the window.....
...Now when checking for collisions with an object, it only needs to check all the other objects in its cell
Your window height is 104 so each collision cell is 104 pixels high. The problem in the capx occurs at y = 520, a multiple of 104. You can see the same problem when the collision happens at 104, 208, 312, etc. It looks like the two sprites are in different collision cells and so no collision is registered.