Different number of dispensers activated depending on orientation of redstone dust

I have a column of 4 dispensers, all facing the same direction (to the right). For demonstration purposes, each is loaded with a different color of shulker box.

In the above screenshot, the dispensers are situated next to a 1-tick pulse generator, but not connected to it. By placing redstone dust on either the diamond block or the gold block, the dispensers are connected to the circuit so that the button causes them to activate.

If redstone dust is placed on the diamond block, all 4 dispensers activate.

If redstone is instead placed on the gold block, only the top 3 dispensers activate.

Since the redstone dust is not powering the dispensers, I'm guessing this is some kind of block update issue, but I don't understand exactly how it's working. What explains this behavior and how can I predict how the dispensers will behave inside of more complex circuits?

I'm using 1.13.1 Java edition.

Solution 1:

This is a block-update bug.

First, the yellow dispenser (color-coded by the color of the shulker box dispensed) is dispensed. Then, because the Redstone runs right into the dispenser, the red and green dispensers fire immediately after, which is why the red shulker is facing upwards while the others aren't.

Next, the blue dispenser updates. The fact that the Redstone is on the diamond block makes the dispenser think it is being powered while it is not. As such, it fires, and the blue shulker box gets dispensed.

This only happens because the Redstone is on the diamond block, 2 blocks away. Yes, this is a bug. I don't look into Minecraft source code, I'd just put the Redstone on the gold until it gets fixed.