The bug

Upon pushing or pulling a light-emitting block (see below for affected blocks), the light flickers off while it is moving. This can cause performance issues due to excessive lighting updates, as well as just be undesirable in general.

How to reproduce

1. Construct the contraption shown in this video if testing redstone lamps, or the simple contraption shown in this screenshot if testing Shroomlights or any other blocks
2. Notice how the redstone lamp flickers every time it is pushed by the piston
3. Replace the redstone lamp with any other light-emitting block from the list below and notice how this same behaviour is present

Affected blocks

• Redstone Lamp (lit)
• Shroomlight
• Sea Lantern
• Glowstone
• Redstone Ore (lit)
• Magma Block

Original description

Using the setup in the screenshot, the lamp will flicker when the lever is pulled.

Glowstone sometimes exhibits this behavior.