local_gb_used wrong in compute_nodes table when using Dell Cinder backend

We have compute nodes with a very small amount of disk so we deploy our instances to Cinder volumes with a Dell backend.
The issue is that when creating instances with a Cinder volume it still gets counted towards the local storage used (local_gb_used in compute_nodes table of the nova database) which results in faulty information on what's actually stored on local disk.

Before:

nova hypervisor-stats
+----------------------+--------+
| Property | Value |
+----------------------+--------+
| local_gb | 425 |
| local_gb_used | 80 |
+----------------------+--------+

cinder list
+--------------------------------------+-----------+---------------------------------------+------+-------------+----------+-------------+
| ID | Status | Name | Size | Volume Type | Bootable | Attached to |
+--------------------------------------+-----------+---------------------------------------+------+-------------+----------+-------------+
+--------------------------------------+-----------+---------------------------------------+------+-------------+----------+-------------+

nova list
+----+------+--------+------------+-------------+----------+
| ID | Name | Status | Task State | Power State | Networks |
+----+------+--------+------------+-------------+----------+
+----+------+--------+------------+-------------+----------+

After booting a new instance with 40 GB cinder volume.

nova hypervisor-stats
+----------------------+--------+
| Property | Value |
+----------------------+--------+
| local_gb | 425 |
| local_gb_used | 120 |

cinder list
+--------------------------------------+-----------+---------------------------------------+------+-------------+----------+--------------------------------------+
| ID | Status | Name | Size | Volume Type | Bootable | Attached to |
+--------------------------------------+-----------+---------------------------------------+------+-------------+----------+--------------------------------------+
| 15345aa2-efc5-4a02-924a-963c0572a399 | in-use | None | 40 | None | true | 29cbe001-4eca-4b2c-972e-c19121a7cc31 |
+--------------------------------------+-----------+---------------------------------------+------+-------------+----------+--------------------------------------+

nova list
+--------------------------------------+--------+--------+------------+-------------+--------------------+
| ID | Name | Status | Task State | Power State | Networks |
+--------------------------------------+--------+--------+------------+-------------+--------------------+
| 29cbe001-4eca-4b2c-972e-c19121a7cc31 | tester | ACTIVE | - | Running | test=192.168.28.25 |
+--------------------------------------+--------+--------+------------+-------------+--------------------+

So the volume is counted as local storage which is wrong and prevents us from knowing if an instance has been
booted on local disk which we need to know since we don't have any local disk for usage.

Anybody got any clues?
Best regards