Bomber+ and Map Switch

I found something strange.

I made a particle that has a side squared and a side round.
Then I used a Rotate to obtain the same particle rotated of 90, 180, 270 degrees.
I don't want to fill the screen with this particle, so I used empty spaces to reduce the percentage of its appearance.

Until I do this using only one Map Switch, everything is ok.
This means 4 real particles and 6 empty spaces.

But I thought to reduce the particle amount more.
So I connected the first Map Switch to a new Map Switch.
And something strange happens.
I get a result composed only of 1 particle type and empty spaces.
But if I reduce the empty spaces, then also other particle types appear.
It is weird.
No matter how many empty spaces I insert, the real particles should always be a mix.

Here is the file.

x.ffxml

But if I reduce the number of empty spaces, I get this :

Logic:
1+ON
2+EMPTY
3+EMPTY
4+EMPTY

Ramlyn, you need a second "Randomizer" (with a different variation) for the second map switch.

There are also other ways to achieve the same result.

This means that the first Map Switch correctly have as result a random choice of all 4 inputs.

When I add the second Map Switch, I should get the random choice of the first Map Switch in the first input. The other 3 inputs are empty, so they should simply represent empty spaces.
And the empty spaces correctly appears.
But why instead of a random choices of the first 4 inputs I get only the first one?

Should not the result be anyway a composition of the different inputs from the first Map Switch + empty spaces in variable number depending on how many empty inputs I use?

Thanks for the explanation emme.