[postgis-users] Polygon validity

[Rykov Denis]

There is following polygon:
POLYGON((317371.62563763 5731575.49932608,
317028.110300846 5731043.43103426,
317028.110300846 5731043.43103426,
316389.822682815 5731138.79331604,
316478.209591618 5731705.00321977,
316478.209591619 5731705.00321977,
317350.223258488 5731584.46661525,
317371.62563763 5731575.49932608))

with two duplicate nodes. When I try to check it with ST_IsValidReason
function I get message
that it is Valid Geometry. Is this OGC compliant? When I try to check
it with QGIS, ArcView or
ArcGIS - I get notice about self intersection. Please explain this situation.