How are fields set as FilterCategory, being indexed?

Hi there, need your help with an (kind of) index issue I can’t solve.

Within WCC users can create folders, which are – in our WCC  environment – labeled ‘Dossier’.

The fieldname is xEDS_Dossier and I made this one available as a filtercategory:

For the user it shows as follows:

One of the users made a mistake in the foldername. For example he typed ‘Farmig’ where he meant ‘Farming’. He made a new folder with the right name and I moved the content to the new folder. However, the name of the new folder never appeared in the category filter. Somehow it holds on to the old (wrong) name. The new name also doesn’t show….