CG_IsSolid(geom) gives the wrong result In PostGIS

[nbvfgh]

We perform the following query on a closed polyhedralsurface：

WITH polyhedralsurface AS (
    SELECT 
        'POLYHEDRALSURFACE Z (((-1 1 -1,1 1 -1,1 -1 -1,-1 -1 -1,-1 1 -1)),
                              ((-1 1 1,-1 -1 1,1 -1 1,1 1 1,-1 1 1)),
                              ((-1 1 -1,-1 1 1,1 1 1,1 1 -1,-1 1 -1)),
                              ((1 1 -1,1 1 1,1 -1 1,1 -1 -1,1 1 -1)),
                              ((1 -1 -1,1 -1 1,-1 -1 1,-1 -1 -1,1 -1 -1)),
                              ((-1 -1 -1,-1 -1 1,-1 1 1,-1 1 -1,-1 -1 -1)))'
     geom
)
SELECT
    CG_IsSolid(geom),
    ST_IsClosed(geom),
    CG_Volume(geom)
FROM polyhedralsurface

-- result : {f,t,0}

But when we converted this polyhedralsurface into a solid, we obtained an unexpected result

WITH solid AS (
    SELECT CG_MakeSolid(
        'POLYHEDRALSURFACE Z (((-1 1 -1,1 1 -1,1 -1 -1,-1 -1 -1,-1 1 -1)),
                              ((-1 1 1,-1 -1 1,1 -1 1,1 1 1,-1 1 1)),
                              ((-1 1 -1,-1 1 1,1 1 1,1 1 -1,-1 1 -1)),
                              ((1 1 -1,1 1 1,1 -1 1,1 -1 -1,1 1 -1)),
                              ((1 -1 -1,1 -1 1,-1 -1 1,-1 -1 -1,1 -1 -1)),
                              ((-1 -1 -1,-1 -1 1,-1 1 1,-1 1 -1,-1 -1 -1)))'
    ) geom
)
SELECT
    CG_IsSolid(geom),
    ST_IsClosed(geom),
    CG_Volume(geom)
FROM solid;

-- expected : {t,t,8};
-- actual   : {f,t,8};

It should be noted that, CG_Volume(geom) computes the volume of a 3D solid,and if it applied to surface (even closed) geometries will return 0. Its return value is 8 here, indicating that geom is not a surface, while CG_IsSolid(geom) returns false. So what type of geometry is geom?

Version Info:

POSTGIS="3.5.0 3.5.0" [EXTENSION] PGSQL="170" GEOS="3.13.0-CAPI-1.19.0" SFCGAL="SFCGAL 1.5.2, CGAL 5.6.1, BOOST 1.84.0" PROJ="8.2.1 NETWORK_ENABLED=OFF URL_ENDPOINT=https://cdn.proj.org USER_WRITABLE_DIRECTORY=C:\WINDOWS\ServiceProfiles\NetworkService\AppData\Local/proj DATABASE_PATH=C:\Program Files\PostgreSQL\16\share\contrib\postgis-3.4\proj\proj.db" (compiled against PROJ 8.13.0) LIBXML="2.12.5" LIBJSON="0.12" LIBPROTOBUF="1.2.1" WAGYU="0.5.0 (Internal)" TOPOLOGY