In your visualModel when accessing the items, try to use .model after the get(), like so:

visualModel.items.get(i).model

@Mephi Hmm, sorry for that. I wasn't aware of it as i have never used it before. So digging in it seems that the attached properties of DelegateModel doesn't seem to work if the delegate is in separate file. Could be a bug I suppose. You can try reporting it here.