Inconsistent behavior for IRIS_TAG_SUPPORT when trying to combine tags

[Excederus]

What happened?

Trying to combine vanilla tags with modded tags to define a group of blocks does not work, however combining modded tags does.

Example:
Does work
block.ID = %supplementaries:candle_holders:dyed/black:candles=2:lit=true
Does not work
block.ID = %candles:dyed/black:candles=2:lit=true
Variations like these also don't work
block.ID = %minecraft:candles:dyed/black:candles=2:lit=true
block.ID = %candles:c:dyed/black:candles=2:lit=true

Screenshots

This is Bliss Shader Commit 482 with colored light/candles enabled and having both entries from the example above in the corresponding block.ID field. The vanilla candle should emit the same amount of light as the modded candle.

Log output

The log is 500MB big due to Every Compat generating alot of blocks with unexpected (missing) tags or Macaw mods using wrong tags (like bridges having the trapdoor tag) that throw massive amounts ignoring Warns about missing properties every time I reload the shader and mods throwing Warns in general for missing textures and stuff.

However here are the first 500 lines of that log:
shortened.log

And also this is what Iris says when trying to find the vanilla+modded combined tags:
[29Nov.2024 16:15:05.753] [Render thread/WARN] [Iris/]: Failed to find the tag candles:dyed/black

Minecraft Version

Minecraft 1.21.1

Iris Version

1.8.0+1.21.1-neoforge

Operating System

Windows 11

What is your GPU?

Nvidia RTX 2070

Additional context

This is the modified block.properties file with the relevant field at line 128 (just renamed to .log)
block.properties.log