Main table: Coloured group indicator for cited entries does not show up consistently anymore

[systemoperator]

Tested with the latest JabRef development version (master branch) on Ubuntu 16.04

Unfortunately, the colored group indicator for cited entries does not show up consistently anymore in the main table: The badge icon with the number of cited entries works, but the colored group indicator in the main table does not show up for most of the cited entries. Sometimes only one, two or four indicators show up. (Updating the group repeatedly or restarting JabRef does not help either.)

@tobiasdiez I strongly suspect that the cause of this issue is connected with the recently conducted performance optimizations of the group functionality (faster group calculations). When reverting back for two weeks, this problem vanishes.

Steps to reproduce the behavior:

1. Create group of cited entries by linking the corresponding .aux file
2. Cite entries in a tex file and build the pdf file
3. Update group of cited entries
4. Observation: Not all indicators show up

[systemoperator]

The issue is caused by commit bc57d22.

[systemoperator]

#6586 slightly reduced the problem, since when the library gets reopened or JabRef gets restarted, then all groups are freshly parsed and properly created now, but the underlying problem still persists in all other cases.

[k3KAW8Pnf7mkmdSMPHz27]

I'll start looking at this

[k3KAW8Pnf7mkmdSMPHz27]

Should an entry's group(s) always show in StandardField.GROUPS? I haven't been able to find any discussion regarding this topic.

[k3KAW8Pnf7mkmdSMPHz27]

What is the expected behaviour for when you have a group selected, so that only entries in the .aux file is shown, and a change occur so that an entry is added/removed?
I am ok with an entry not being removed from the view (as it is indicated by the group color anyway, as shown in the screenshot below), but what about when they are added?

[k3KAW8Pnf7mkmdSMPHz27]

I am assuming that it should behave in the same way as for searches (the bib entry gets added/removed immediately but the entry editor still show the entry if it was selected)