Today physical locator creation is driven from controller , but not deletion.
Physical locator can be deleted from the device database , when the device sees no references to it.

This is posing some problems with subsequent creations.
When mcast mac1 is created along with locator1

The operational datastore contains locator1 and its uuid.

Now if the following updates come.
at time T1)Delete mcast mac1
at time T2)Insert mcast mac2 ( referring to locator1 )

First odl controller will fire delete mcast mac1 to device.
The device acknowledges success for the transaction.

In the background
The device also deletes locator1 as its only reference is gone and sends an update to the controller ( let us say this sending the delete update to controller is delayed by a sec ).

Before that previous event happens if Insert mcast mac2 event comes, controller uses the uuid of locator1 to create mac2.
This insertion of mac2 fails with error saying such a foreign key does not exist.

Controller has no clue that device is going to delete locator1 and went ahead used its uuid to create mac2 which resulted in this error.