Basically, the blocks in #wither_immune should be immune to the Wither, be it the starting explosion or the wither heads that hit the block.

However, this is actually not the case.
The blocks already existed in the tag is explosion resistant, so they appear to be immune to the wither,
but when you add a new block (say, dirt) the dirt block not only is not immune to the Wither's starting explosion, but wither heads easily make holes in the block itself.

So it's not the block tag that's protecting the blocks from the wither, but rather the blocks themselves.

So are block tags lying to us? Clearly.

Please fix this, I made it as short and as understandable as possible. Please.
Even though Mojang has a thing with not fixing bugs that don't affect vanilla gameplay ...