Despite acting like other types of grass, which indeed are replaceable, bushes are not considered replaceable. This also results in them being missing from the #minecraft:replaceable block tag, which prevents them from acting as enchantment power transmitters.
Firefly bushes are also not replaceable with similar effects; this issue is described separately in MC-279915.
Expected results
Bushes can be replaced by other blocks and be placed between bookshelves and enchanting tables without affecting the enchantment choices.
Actual results
Other blocks get placed on the side of bushes, and enchantment possibilities are affected by the placement of a rogue bush.
Comments 3
Just for clarity, the tag does not control what can be replaced, it just lists blocks that can be, but no behavior is tied to it (other than being ignored by enchanting table bookshelf check).
Can confirm.