When migrating a project to 2.5 it works fine, but when I create it new in 2.5 it does not work (also not when creating a test-project). I create a form with a picture uploader and a picture viewer; The Main entity has a 1-0 relation with the entity Pictures holding the pictures. That last entity has a generalization with system.image. The DataView consist of the Main entity holding a sub-DataView for the entity Pictures. The pictures never are stored in the table. What goes wrong?
I did something similar in the last couple of days and it works for me. I have a 1-1 relationship defined between main entity and picture entity. Try that and see if it works.
In short; I did not store the association to the image. In 2.4 this construction works, since nested dataviews (in the edit form) automatically create objects and set associations. But in 2.5 this is no longer the case (see the migration notes for more details) and you need to set the association 'by hand'.