This might very well be WAI, but reporting just in case.

Observed result:

Wither roses damage entities when they are inside the block of the wither rose.

Expected result:

Wither roses only damage entities that intersect with the bounding box of the wither rose.

How to reproduce:

The easiest way to reproduce this is to simply walk near a wither rose and observe when you take damage.

For a clearer reproduction, see the image below. Note that wither roses are placed at different positions inside the block depending on the coordinates, so you need to find a position where it is far enough to one side for this setup to work.

Clones MC-199846 which was marked as duplicate of MC-1133 but this issue remains.