I was building a diagonal of downward pistons to push some other pistons on top of glowstone, and happened upon this.

I powered all of the pistons from above using a zig-zag of redstone and a wooden button. Each piston has a solid block directly on top of it, and each of those blocks are being powered by redstone dust on top of them.

The result was that for the pistons being powered by redstone power level 9+, there was no problem. Those extended and retracted as expected. But two pistons at the end are getting stuck consistently. They are powered by redstone power level 7 and below.

The pistons that stay extended are in BUD mode. If I place a block next to them, they retract. But it makes no sense why they would lock out in BUD mode, and only the ones on the low-power half of the circuit. Very strange.

I've attached screenshots, which also include block status data of the redstone while powered.

Again, to clarify, each piston has a block powered by redstone directly above it. They do also all have at least one block powered on the upwards-diagonal, which is a known quasi-connection configuration, but only the power 7 and below pistons are stuck.

I can provide the world upon request by a Mojang member if they cannot reproduce on their own. It is only a small creative world.