JabRef 3.7dev--snapshot--2016-08-31--master--4913665
windows 10 10.0 amd64
Java 1.8.0_101

Steps to reproduce:

1. Start with a database that contains a few articles and a few groups
2. Assign an article to a group, to which it had not been assigned previously
3. The article is assigned to the new group (confirmed by checking the respective bibtex field), but it is not displayed properly in the "main table/database view" of Jabref. Usually, all entries of a group have a white background, while those which do not belong to the group, have a grey background. Furthermore, all entries of a group are shown at the top of the "main table/database view", while non-members are shown below the group members. The new entry, however, is not displayed in such a way - instead, it is still treated as a non-member, i. e. it has a grey background and it is not grouped together with other group members at the top of the "main table/database view".
4. If another group is selected and then again the previous group, the newly assigned article is displayed correctly as the member of the group with white background and on top of non-group members.