Custom blocks using vanilla textures do not match vanilla blocks in game.

Partner Rank: 2
 
Verification builds:
1.16.100, 1.16.200 
 
Summary:
When creating a custom block using vanilla textures. Some custom blocks do not match their vanilla counterparts in the way they appear in game.

Impact:
This will impact our future content as this stops us from being able to create similar blocks to vanilla so we can use them in our build to track players and run commands. 
 
Repro Steps:

1. Create a custom block using the sea lantern texture and make sure it has light emission of 1.0.
2. Open a world with the custom block.
3. Give and then place a vanilla sea lantern.
4. Give and place the custom sea lantern block next to it.

 
Observed Results:
The custom block will be visibly darker compared to the default vanilla block.
 
Expected Results:
The custom block should match their vanilla block counterpart.

Screenshots/Videos attached: Yes