Redstone blocks, with an air gap below it, activate certain blocks and keep it activated, these being pistons, dispensers, and droppers, only when the activated block gets a block update.

The pistons only require a block update if placed before the redstone block

Steps to reproduce:

1. place a redstone block above a dispenser (or affected block), with one air-gap between them

2. Update the dispenser (or affected block) by placing a block next to it

I put a water bucket in the dispenser for visual reference sake

It will stay triggered until you break the redstone block and update the affected block again

I was building some convoluted build where a dispenser with a water bucket was dispensing for no reason, and wasnt accepting other redstone output. There was nothing that should have activated it, yet it was, and only when i gave it a block update by breaking or placing something around it. Turns out it was a redstone block above it, that had an air gap between it. I tested and found out it was only certain block specific, with only effecting droppers, dispensers, and pistons to my knowledge.  I do not believe this is intended, and fixing would be greatly appreciated. For now, my water airlock design will have to do some minor renovations.