Regarding field not pulling information on the custom entity record automatically when creating a communication for custom entity.
The uncustomised regarding field only works correctly on primary entities.
You must press the magnifying glass and search for custom entity record.
This issue is not reproducible in Sage CRM 7.3d.
Create a new regarding field similar to the original (I called it 'Regarding test entity').
Change the search entity selection to testEntity and the default to 'Search with current custom entity'.
Pick testEntity as the tied field.
Add this field to the commWebPicker screen.