Items auto-generated for custom blocks do not inherit their block’s tags. Items using the replace_block_item feature of the minecraft:block_placer component, however, do. This behavior is inconsistent and cannot be disabled.

Demonstration

Below shows this behavior, as it is logged from scripting (ItemStack#getTags()):

2 blocks are defined. Both have the bug_tags:example block tag. Only the block with the item override inherits it.

Reproduction

This example is taken from the behavior pack in the following world attached for convenience:

This world can be opened (in Minecraft Preview) for inspection or unzipped to access the code associated with such. Any button press in this world triggers a log to fire listing the item tags as shown in the demonstration. Ensure the content log is enabled.