Is this a bug? Im really tired of readding and removing "favorite defaults" (that nobody asked you to put in in the first place) at every launch.
So the only way to "solve" is to create new tag, ok ty.

There is a brush preset tag called '* My Favorites' with brush presets already labelled with that tag and yes, there are bugs in the tagging system which are being worked on as part of a wider Resources rewrite.

You don't have to use that tag if you don't want to. You can create new tags called 'Mara Favorites' or 'Mara Sketching' etc and add those tags to any brush preset.
Why do you re-add and remove 'favourite defaults'? (I assume you mean '* My Favorites'.)