Every other Dispenser/Dropper does not get powered by redstone through blocks

When powering a line of Dispensers/Droppers through a block with a decreasing signal strength, only every other Dispenser/Dropper (plus the last three) are activated.

Steps to Reproduce:
1. Place a straight line of 15 Dispensers or Droppers.
2. Place a block on top of each of them.
3. Place redstone dust on top of those blocks.
4. Place a block from one of the redstone dusts at the ends, and put a button on that block.
5. Push the button.

Expected Results:
All of the Dispensers/Droppers should be activated.

Observed Results:
Half of the Dispensers/Droppers are activated.