When creating a PostGIS table (e.g. 'lakes') in the DB Manger a primary key ('lakes_pkey'), a index ('sidx_lakes_geom) and a sequence ('lakes_gid_seq') are also created.
But when renaming the table (e.g. 'lakes_2015'), the constraint, the index and the sequence don't get new names.
So it's not possible to create a new table named 'lakes' after renaming the original table 'lakes'.
Error: Relation „sidx_lakes_geom“ already exists
Is this a bug? (https://hub.qgis.org/issues/13823)