I attempted to created a new release and release group, for an existing artist. At the final step to actually save the information, there was an unusually long pause and then this message appears in red:

23505 DBD::Pg::st execute failed: ERROR: duplicate key value violates unique constraint "medium_uniq" DETAIL: Key (release, "position")=(5732872, 1) already exists. [for Statement "INSERT INTO medium (position,release,format,gid,name) VALUES (?,?,?,?,?) RETURNING id" with ParamValues: 1='1', 2='5732872', 3='12', 4='8e8b9f98-aea7-4b76-b3e3-7a933e087b2c', 5='']