diff --git a/src/game_display.cpp b/src/game_display.cpp
index 3f2cca18212..25528b2d57e 100644
--- a/src/game_display.cpp
+++ b/src/game_display.cpp
@@ -265,7 +265,11 @@ void game_display::pre_draw() {
 	previous_invalidated_.swap(invalidated_);
 	invalidated_.insert(previous_invalidated_.begin(),previous_invalidated_.end());
 	// call invalidate_animation again to deal with new conflict arising from the merge
-	invalidate_animations();
+	// no conflict, if a hex was invalidated last turn but not this turn, then 
+	// * case of no unit in neighbour hex=> no propagation
+	// * case of unit in hex but was there last turn=>its hexes are invalidated too
+	// * case of unit inhex not there last turn => it moved, so was invalidated previously
+	// invalidate_animations();
 	process_reachmap_changes();
 	/**
 	 * @todo FIXME: must modify changed, but best to do it at the
diff --git a/src/unit_animation.cpp b/src/unit_animation.cpp
index ec940a86d97..a14fbc4f1f6 100644
--- a/src/unit_animation.cpp
+++ b/src/unit_animation.cpp
@@ -632,7 +632,8 @@ unit_animation::particule::particule(
 		accelerate(true),
 		parameters_(cfg,frame_string),
 		halo_id_(0),
-		last_frame_begin_time_(0)
+		last_frame_begin_time_(0),
+		invalidated_(false)
 {
 	config::const_child_itors range = cfg.child_range(frame_string+"frame");
 	config::const_child_iterator itor;
@@ -767,11 +768,11 @@ void unit_animation::redraw(const frame_parameters& value)
 		anim_itor->second.redraw( value,src_,dst_);
 	}
 }
-bool unit_animation::invalidate(const frame_parameters& value) const
+bool unit_animation::invalidate(const frame_parameters& value)
 {
 
 	bool result = false;
-	std::map<std::string,particule>::const_iterator anim_itor =sub_anims_.begin();
+	std::map<std::string,particule>::iterator anim_itor =sub_anims_.begin();
 	result |= unit_anim_.invalidate(value,src_,dst_,true);
 	for( /*null*/; anim_itor != sub_anims_.end() ; anim_itor++) {
 		result |= anim_itor->second.invalidate(value,src_,dst_);
@@ -780,6 +781,7 @@ bool unit_animation::invalidate(const frame_parameters& value) const
 }
 void unit_animation::particule::redraw(const frame_parameters& value,const map_location &src, const map_location &dst, const bool primary)
 {
+	invalidated_=false;
 	const unit_frame& current_frame= get_current_frame();
 	const frame_parameters default_val = parameters_.parameters(get_animation_time() -get_begin_time());
 	if(get_current_frame_begin_time() != last_frame_begin_time_ ) {
@@ -789,11 +791,13 @@ void unit_animation::particule::redraw(const frame_parameters& value,const map_l
 		current_frame.redraw(get_current_frame_time(),false,src,dst,&halo_id_,default_val,value,primary);
 	}
 }
-bool unit_animation::particule::invalidate(const frame_parameters& value,const map_location &src, const map_location &dst, const bool primary ) const
+bool unit_animation::particule::invalidate(const frame_parameters& value,const map_location &src, const map_location &dst, const bool primary )
 {
+	if(invalidated_) return false;
 	const unit_frame& current_frame= get_current_frame();
 	const frame_parameters default_val = parameters_.parameters(get_animation_time() -get_begin_time());
-	return current_frame.invalidate(need_update(),get_current_frame_time(),src,dst,default_val,value,primary);
+	invalidated_ = current_frame.invalidate(need_update(),get_current_frame_time(),src,dst,default_val,value,primary);
+	return invalidated_;
 }
 
 unit_animation::particule::~particule()
diff --git a/src/unit_animation.hpp b/src/unit_animation.hpp
index 6305ecfd257..b6b4b7efff3 100644
--- a/src/unit_animation.hpp
+++ b/src/unit_animation.hpp
@@ -59,7 +59,7 @@ class unit_animation
                 void restart_animation();
 		int get_current_frame_begin_time() const{ return unit_anim_.get_current_frame_begin_time() ; };
 		void redraw(const frame_parameters& value);
-		bool invalidate(const frame_parameters& value ) const;
+		bool invalidate(const frame_parameters& value );
 
 	friend class unit;
 	protected:
@@ -77,14 +77,15 @@ class unit_animation
 				accelerate(true),
 				parameters_(),
 				halo_id_(0),
-				last_frame_begin_time_(0)
+				last_frame_begin_time_(0),
+				invalidated_(false)
 				{};
 			explicit particule(const config& cfg,const std::string frame_string ="frame");
 			virtual ~particule();
 			bool need_update() const;
 			void override(int start_time,const std::string highlight="", const std::string blend_ratio ="",Uint32 blend_color = 0,const std::string offset="");
 			void redraw( const frame_parameters& value,const map_location &src, const map_location &dst, const bool primary=false);
-			bool invalidate(const frame_parameters& value,const map_location &src, const map_location &dst,  const bool primary = false) const;
+			bool invalidate(const frame_parameters& value,const map_location &src, const map_location &dst,  const bool primary = false);
 			void start_animation(int start_time, bool cycles=false);
 			const frame_parameters parameters(const frame_parameters & default_val,bool primary) const { return get_current_frame().merge_parameters(get_current_frame_time(),parameters_.parameters(get_animation_time()-get_begin_time()),default_val,primary); };
 			bool accelerate;
@@ -94,6 +95,8 @@ class unit_animation
 			frame_builder parameters_;
 			int halo_id_;
 			int last_frame_begin_time_;
+			// optimisation
+			bool invalidated_;
 
 	};
 		t_translation::t_list terrain_types_;