In the toolbar brushes and co there is a dropdown to chose a paint preset just right to the brush parameters.

In this dropdown, if you right click on a brush and try to add a new tag or assign one, it will disappear and not work.

I have to use the the brush preset panel to make it work.

btw the search field in that panel is so efficient that if you prefix your brushes correctly, it will act like tags.
It's very useful since when I import a preset, the tag assignment is not imported so I have to reassign the brushes to their tags every time (can't use bundles, they have other issues that make merging them together to update them quite painfull)

Reproducible: Always

Steps to Reproduce:
1.Open the paintToPreset dropdown in the brush and co
2. right click a brush
3. try to assign a new or existing tag to it

Actual Results:  
the dialog disappears and nothing happens

Expected Results:  
tags are happily assigned

windows 10
krita 3.0 portable