I noticed some problems in assigning items to semantic groups and non-semantic groups. Whenever my item is linked to a non-semantic group and I want to assign additionally a semantic group, the non-semantic group gets unlinked, and vice versa.
Furthermore when I create an item it does not show up in the dialog where you can select new members for a group.
Is there still an issue in v4.1.0M2 or is my json-db becoming corrupt?
Show the steps you are taking with screenshots and/or animated screen capture.
Make sure you try it in a browser other than Firefox. There is a caching issue in Firefox which can cause strange behaviors like this.
If the DB becomes corrupt, your Items would be completely gone. This is a UI issue I think.