Clear placed mines queued fields too.

OpenRA.Mods.Cnc/Activities/LayMines.cs

@@ -39,7 +39,6 @@ namespace OpenRA.Mods.Cnc.Activities
 			movement = self.Trait<IMove>();
 			rearmableInfo = self.Info.TraitInfoOrDefault<RearmableInfo>();
 			this.minefield = minefield;
-			ChildHasPriority = false;
 		}
 
 		protected override void OnFirstRun(Actor self)
@@ -60,13 +59,6 @@ namespace OpenRA.Mods.Cnc.Activities
 
 		public override bool Tick(Actor self)
 		{
-			// Remove cells that have already been mined
-			minefield.RemoveAll(c => self.World.ActorMap.GetActorsAt(c)
-				.Any(a => a.Info.Name == minelayer.Info.Mine.ToLowerInvariant()));
-
-			if (!TickChild(self))
-				return false;
-
 			returnToBase = false;
 
 			if (IsCanceling)
@@ -109,6 +101,14 @@ namespace OpenRA.Mods.Cnc.Activities
 			return true;
 		}
 
+		public void CleanPlacedMines(Actor self)
+		{
+			// Remove cells that have already been mined
+			if (minefield != null)
+				minefield.RemoveAll(c => self.World.ActorMap.GetActorsAt(c)
+					.Any(a => a.Info.Name == minelayer.Info.Mine.ToLowerInvariant()));
+		}
+
 		public override IEnumerable<TargetLineNode> TargetLineNodes(Actor self)
 		{
 			if (returnToBase)

OpenRA.Mods.Cnc/Traits/Minelayer.cs

@@ -37,7 +37,7 @@ namespace OpenRA.Mods.Cnc.Traits
 		public object Create(ActorInitializer init) { return new Minelayer(init.Self, this); }
 	}
 
-	public class Minelayer : IIssueOrder, IResolveOrder, ISync, IIssueDeployOrder, IOrderVoice
+	public class Minelayer : IIssueOrder, IResolveOrder, ISync, IIssueDeployOrder, IOrderVoice, ITick
 	{
 		public readonly MinelayerInfo Info;
 
@@ -115,6 +115,13 @@ namespace OpenRA.Mods.Cnc.Traits
 			}
 		}
 
+		void ITick.Tick(Actor self)
+		{
+			if (self.CurrentActivity != null)
+				foreach (var field in self.CurrentActivity.ActivitiesImplementing<LayMines>())
+					field.CleanPlacedMines(self);
+		}
+
 		string IOrderVoice.VoicePhraseForOrder(Actor self, Order order)
 		{
 			if (order.OrderString == "PlaceMine" || order.OrderString == "PlaceMinefield")