Rocks'n'Diamonds

So I was making a level for my 15x15 mini levels levelset, and here what it looks like: What I expected from making the level is what the title suggests, I expected the movements of the Spaceships to exactly mirror the Bugs' movement at the other side, but a notable change in the Spaceships' side occurs just 2 seconds in. I'm not exactly sure what makes this work, but it just tells me that it doesn't exactly mirror the bugs' movements at the opposite side.

Is this an intentional quirk in the Emerald Mine engine? Just like having a boulder hit on a diamond that's on top of the the player not being destroyed being that quirk type of thing? Here's the level itself:

Only guessing, from past observations: I think their individual behavior algorithms are mirror-identical, but perhaps the order in which their actions are considered are not. I think each one's move may be considered in sort of a raster order, so if the move of object-to-the-left is going to occupy the space which would otherwise have been moved into by object-to-the-right, the left one 'wins'.

I didn't download your level (currently at work with no RnD to run :)