[postgis-users] Geometry type returned by ST_Buffer

[Sean]

I have two tables of MULTIPOLYGONS to which I apply a negative buffer
and relate to see how they overlap.  (The buffer is necessary to
accommodate errors where the boundaries should coincide.)

With PostGIS 1.4, this worked:

ST_Relate(ST_Buffer(geom1, -.0005), ST_Buffer(geom2, -.0005),
'T********')

I upgraded to PostGIS 1.5 and now I get the error:

ERROR: Relate Operation called with a LWGEOMCOLLECTION type.  This is
unsupported.

All geometries in the tables return geometry type MULTIPOLYGON.  It
seems that ST_Buffer on the MULTIPOLYGONs returns geometries of type
POLYGON, MULTIPOLYGON and GEOMETRYCOLLECTION.  Am I doing something
wrong or is this a bug?

System info:
PostgreSQL 8.3
POSTGIS="1.5.1" GEOS="3.2.0-CAPI-1.6.0" PROJ="Rel. 4.6.1, 21 August
2008" LIBXML="2.7.6" USE_STATS
Windows XP

Thanks,

   Sean