Setting foreign key to null by PropertyEntry.CurrentValue deletes entity

[majbo]

Given is an entity with a self-referencing relationship that is configured with DeleteBehavior.Cascade.

public class Tag
{
    public Guid Id { get; set; }
    public string Name { get; set; } = null!;
    public Tag? SynonymFor { get; set; }
    public Guid? SynonymForId { get; set; }
    public IEnumerable<Tag> Synonyms { get; set; } = null!;
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Tag>().HasMany(p => p.Synonyms)
        .WithOne(p => p.SynonymFor)
        .OnDelete(DeleteBehavior.Cascade);
}

When setting the foreign key to null using the PropertyEntry.CurrentValue, the EntityEntry.State changes to Deleted and thereby the call to SaveChanges deletes the entity.

var barTag = context.Tags.Single(p => p.Name == "Bar");
var barEntry = context.Entry(barTag);
barEntry.Property(nameof(Tag.SynonymForId)).CurrentValue = null;

I created a simple app here: (https://github.com/majbo/EFCascadeDeleteError)
Execute the unit tests. The first one succeeds, it sets the foreign key directly on the entity. The second one fails, it sets the foreign key using PropertyEntry.CurrentValue.

Include provider and version information

EF Core version: 5.0.8
Database provider: Microsoft.EntityFrameworkCore.Sqlite
Target framework: .NET 5.0
Operating system: Windows 10
IDE: Rider 2021.1.5

[ajcvickers]

Note for triage: this appears to be a bug. Setting the FK to null should trigger delete orphans behavior when the relationship is set to cascade and delete orphans timing has not been changed. However, the relationship here is not required, which is causing this to be behave inconsistently.