Found Buried Treasure but cannot find a corresponding treasure map

The Coastal Village Seed, -1813740965 (created v1.5.0.4), Survival Mode; Infinite Size. I have found buried treasure, but I cannot find Ruins or a Shipwreck with a treasure map which points to the buried treasure. As an example: I accidentally found a buried treasure at coordinates x=1608, y=60, z=72; but I cannot find a treasure map from the normal sources (shipwreck or ruins). I try to collect a treasure map for each buried treasure.

I am not sure if this is a bug or designed this way. I have found other buried treasures which have no corresponding treasure maps in the same world.