Custom Blocks still don't spawn in structures in 1.8.1

Status
Works as designed
Issue description

I don't think it was fixed. I just tested it with a small structure full of custom blocks, but only the vanilla blocks spawned in. Is it perhaps because I was using blocks that I made and not things like spawners? This is supposed to have been fixed. I understand if busy schedules get in the way, but it was said to be fixed in this part of the changelog for 1.8.1:

  • [Bugfix #44854] Custom blocks in generated structures not spawning in exported mods

 

Is my problem different from the fix and not fixed yet or something?

Is this a problem with the structure block in Minecraft itself?

 

Below is an image of what happens. The structure is supposed to be made of colorful bricks in my mod. Tested this in both the test environment and in regular Minecraft.

Issue comments

Open test environment mod client (run Minecraft in MCreator) and use a structure block (https://minecraft.gamepedia.com/Structure_Block) to save a structure with your custom blocks. Then in MCreator, go to Structures tab in sidetabs of workspace and click Import structure from Minecraft or something in these lines. Select your structure and it will be imported in MCreator.

The custom blocks/items/... need to have testenvironmentmod preffix, so make sure this is the modid you use when exporting the structure. The best way to do this is to export your structure from the test environment Minecraft client.

Related: https://mcreator.net/forum/44186/generate-structure-custom-blocks-180