A player discovered an unusual interaction between Grimstroke’s Soulbind and Legion Commander’s Duel. If you apply Soulbind to Warlock, Visage, or another character with a summoned creature, LC will be able to get additional damage after a duel not only for killing the hero, but also for killing their summon (Reddit).
Reddit users disagreed on whether to consider this interaction of abilities a bug. They noted that the same bear at Lone Druid will forever retain bonus damage if it kills Legion Commander during a duel. On the other hand, Arc Warden clone's similar bonus damage is zeroed out as soon as the copy is recalled.
In the discussion, people recalled that Soulbind and Duel can only be used on heroes, and interaction with other creatures at least contradicts the description of the skills. Users believe that the developers simply did not foresee such a combination, and in the future Valve will fix the error.