Duel bug...

It's a simple fix, apply patch:

diff --git a/src/game/WorldHandlers/SpellEffects.cpp b/src/game/WorldHandlers/SpellEffects.cpp
index 73b58bf..24f77ad 100644
--- a/src/game/WorldHandlers/SpellEffects.cpp
+++ b/src/game/WorldHandlers/SpellEffects.cpp
@@ -3937,6 +3937,12 @@ void Spell::EffectDuel(SpellEffectIndex eff_idx)
     Player* caster = (Player*)m_caster;
     Player* target = (Player*)unitTarget;
 
+	if (caster->duel)
+		caster->DuelComplete(DUEL_INTERRUPTED);
+
+	if (target->duel)
+		target->DuelComplete(DUEL_INTERRUPTED);
+
     // caster or target already have requested duel
     if (caster->duel || target->duel || !target->GetSocial() || target->GetSocial()->HasIgnore(caster->GetObjectGuid()))
         { return; }