ST_ConcaveHull returns polygon with holes despite allow_holes set to false

[nbvfgh]

Considering following query:

WITH data AS(
	SELECT ST_GeomFromText('POLYGON ((0 0, 1 0, 2 1, 1 1, 0 0),(0.2 0.1, 0.5 0.4, 0.5 0.3,0.2 0.1))'
	) geom
)
SELECT ST_AsText(ST_ConcaveHull(geom, 0.3, false))
	   from data;

-- expected:{ POLYGON((0 0,1 0,2 1,1 1,0 0))}
-- acutal:  { POLYGON((0 0,1 0,2 1,1 1,0 0),(0.2 0.1,0.5 0.4,0.5 0.3,0.2 0.1)) }

We calculate the concave hull of a Polygon With hole，and set param_allow_holes = false.
But the result still contains a hole when the optional param_allow_holes argument is specified as false, which seems to be unexpected.

The original input and result are shown in the following figure：