Duplicate rows in roads/line/polygon tables ?

[cquest]

I've found a few duplicated rows in the planet_osm_roads table on one of the world databases.
This database is quite old, and has been updated using diff for several years.

They all happened on geometries originating from relations (boundaries, etc).
I've not yet checked the line and polygon tables.

I discovered that by trying to create a unique index on these tables in order to be able to use pg_repack to vacuum/cluster these tables without global lock.