The genre filter options can give unexpected results, where less genres are used then the maximum number of genres configured, even though more genres are available that would match the criteria. There are two distinct issues:

1. The genre list is reduced to the maximum allowed number of items before filters are applied.
2. The max. count (used to filter out genres by minusage threshold) is taken over the entire list. It better should ignore filtered out genres.

Examples:

You have the following tags with counts:

Pop: 5, Blues: 7, Rock: 5, Psychedelic: 4

You have a filter "-pop"

Number of genres is limited to max. 3.

Picard takes the first most used tags (Blues, Pop, Rock), then applies the filters.

Result: Blues, Rock

Better would be to ignore the filtered genre and use: Blues, Rock, Psychedelic

You have the following tags with counts:

Pop: 5, Blues: 11, Rock: 20, Psychedelic: 9

You have a filter "-rock"

The threshold is set to 50%.

Picard takes the first most used tags (Rock, Blues, Pop), then applies the filters and the threshold. For the threshold the most used genre (Rock=20) is used as the reference max. count, even if it gets removed.

Result:  Blues

Better would be to ignore the filtered genre. Then the max. count would be Blues=11 and the result be: Blues, Psychedelic