For the items used in the first explorer pane, you never stored the association to the image, so there was a modeling error in there, the widget behaved correctly (I will send you the fix by email). As you stated, 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'.
For the second explorer pane, the rc-1 implementation of the widgets configuration (Entity object is image) was not compatible with the newer 2.5 releases anymore. I published a new version of the widget in the Appstore which is compatible.
Are you using the same version of the modeler as stated in the Appstore? I recall that i updated the widget for API changes in rc-2. If you enable firebug, and see 404 errors in the NET tab, your widget does not match the modeler version.
Are you sure the images are saved correctly? I just tried using the explorer pane with an entity generalized on System.Image and it work as expected for me.
Maybe you can set the attribute HasContents as a display attribute, to make sure the images are connected to the entity.
Also, have you tried the green Refresh button on the far right in the toolbar of the pane?