Observing a dispenser has inconsistent behavior in a vertical configuration

A vertical stack with:

• switch (any block that changes state)
• observer (facing downward)
• dropper (with e.g. water bucket)
• observer (facing downward)
• solid block (e.g. stone)

Will tick the observer twice; one tick on, three ticks off, one tick on. Removing the solid block results in the expected behavior of a single tick.

The same arrangement rotated onto its side has the same behavior either way.

Video:
https://youtu.be/XD6hLOlXTyY

Creative single-player world attached.