Database module: mixed up entries in separate groups mode for teachers

There is an issue with the database activity (mod data) using separate groups for any role with editing rights in a course (teacher, admin, ...) .

Following scenario:
1. Database activity is set up in mode "separate groups"
2. Database fields are set up to upload files
3. Students are assigned to groups
4. Students upload files into the database activity within their assigned group

From a student perspective everything works fine and each group is only able to see files uploaded within their own group.
For a teacher role, there is a problem with the displayed entries per group:

Selecting "All participants" or any of the groups in the "list view" results in a list of random entries being shown from diverse groups. Switching from one group to the next leads to different more or less random results.

To reproduce:
1. Create a course with a teacher and at least two groups A and B (assign a demo student to each group )
2. Create a database activity in separate groups mode and add a new field (e.g. file)
3. Set up list view
4. Let each student add an entry to the database for his/her group
5. Log in as teacher, open the list view of the database and select group B in the drop down menu -> all files are shown, not only those of group B
6. Select "All participants" -> only file of group B is shown