Index: binaries/data/mods/public/gui/session/unit_commands.js
===================================================================
--- binaries/data/mods/public/gui/session/unit_commands.js	(revision 12061)
+++ binaries/data/mods/public/gui/session/unit_commands.js	(working copy)
@@ -505,7 +505,7 @@
 				grayscale = "grayscale:";
 			}
 			
-			if (guiName == RESEARCH && !Engine.GuiInterfaceCall("CheckTechnologyRequirements", entType))
+			if (guiName == RESEARCH && !Engine.GuiInterfaceCall("CheckTechnologyRequirements", { "tech": entType, "researcher": unitEntState.id }))
 			{
 				button.enabled = false;
 				button.tooltip += "\n" + GetTechnologyData(entType).requirementsTooltip;
@@ -520,7 +520,7 @@
 				{
 					grayscale = "";
 					button1.enabled = true;
-					if (guiName == RESEARCH && !Engine.GuiInterfaceCall("CheckTechnologyRequirements", entType1))
+					if (guiName == RESEARCH && !Engine.GuiInterfaceCall("CheckTechnologyRequirements", { "tech": entType1, "researcher": unitEntState.id }))
 					{
 						button1.enabled = false;
 						button1.tooltip += "\n" + GetTechnologyData(entType1).requirementsTooltip;
Index: binaries/data/mods/public/simulation/components/GuiInterface.js
===================================================================
--- binaries/data/mods/public/simulation/components/GuiInterface.js	(revision 12061)
+++ binaries/data/mods/public/simulation/components/GuiInterface.js	(working copy)
@@ -521,14 +521,14 @@
 };
 
 // Checks whether the requirements for this technology have been met
-GuiInterface.prototype.CheckTechnologyRequirements = function(player, tech)
+GuiInterface.prototype.CheckTechnologyRequirements = function(player, data)
 {
 	var cmpTechnologyManager = QueryPlayerIDInterface(player, IID_TechnologyManager);
 	
 	if (!cmpTechnologyManager)
 		return false;
 	
-	return cmpTechnologyManager.CanResearch(tech);
+	return cmpTechnologyManager.CanResearch(data.tech, data.researcher);
 };
 
 GuiInterface.prototype.PushNotification = function(notification)
Index: binaries/data/mods/public/simulation/components/ProductionQueue.js
===================================================================
--- binaries/data/mods/public/simulation/components/ProductionQueue.js	(revision 12061)
+++ binaries/data/mods/public/simulation/components/ProductionQueue.js	(working copy)
@@ -233,7 +233,7 @@
 			// Tell the technology manager that we have started researching this so that people can't research the same 
 			// thing twice.
 			var cmpTechMan = QueryOwnerInterface(this.entity, IID_TechnologyManager);
-			cmpTechMan.StartedResearch(templateName);
+			cmpTechMan.StartedResearch(templateName, this.entity);
 
 			this.queue.push({
 				"id": this.nextID++,
@@ -306,7 +306,26 @@
 		// Mark the research as stopped if we cancel it
 		if (item.technologyTemplate)
 		{
-			var cmpTechMan = QueryOwnerInterface(this.entity, IID_TechnologyManager);
+			// item.player is used as this.entity's owner may be invalid (deletion, etc.)
+			var cmpTechMan = QueryPlayerIDInterface(item.player, IID_TechnologyManager);
+			var template = cmpTechMan.GetTechnologyTemplate(item.technologyTemplate);
+			var removed = item.technologyTemplate;
+			if (template.pair)
+				removed = template.pair;
+
+			// Recurse to remove any technologies that supersede this one.
+			for (var j = i; j < this.queue.length; ++j)
+			{
+				if (!this.queue[j].technologyTemplate)
+					continue;
+
+				var queued = cmpTechMan.GetTechnologyTemplate(this.queue[j].technologyTemplate);
+				if (!queued.supersedes && queued.pair)
+					queued = cmpTechMan.GetTechnologyTemplate(queued.pair);
+
+				if (queued.supersedes == removed)
+					this.RemoveBatch(this.queue[j--].id);
+			}
 			cmpTechMan.StoppedResearch(item.technologyTemplate);
 		}
 		
Index: binaries/data/mods/public/simulation/components/TechnologyManager.js
===================================================================
--- binaries/data/mods/public/simulation/components/TechnologyManager.js	(revision 12061)
+++ binaries/data/mods/public/simulation/components/TechnologyManager.js	(working copy)
@@ -90,7 +90,7 @@
 };
 
 // Checks the requirements for a technology to see if it can be researched at the current time
-TechnologyManager.prototype.CanResearch = function (tech)
+TechnologyManager.prototype.CanResearch = function (tech, researcher)
 {
 	var template = this.GetTechnologyTemplate(tech);
 	if (!template)
@@ -98,14 +98,29 @@
 		warn("Technology \"" + tech + "\" does not exist");
 		return false;
 	}
-	
-	// The technology which this technology supersedes is required
+
+	// A technology can be researched if a technology that it supersedes
+	// is already being researched at the same building.
 	if (template.supersedes && !this.IsTechnologyResearched(template.supersedes))
+	{
+		if (!researcher)
+			return false;
+
+		var oldtech = this.GetTechnologyTemplate(template.supersedes);
+
+		// Pairs are handled specially, as it's their members that are
+		// researched, not the actual pairs themselves.
+		if (oldtech.top)
+		{
+			if ((this.GetResearcher(oldtech.top) || this.GetResearcher(oldtech.bottom)) != researcher)
+			return false;
+		}
+		else if (this.GetResearcher(template.supersedes) != researcher)
+			return false;
+	}
+	if (template.pair && !this.CanResearch(template.pair, researcher))
 		return false;
 	
-	if (template.pair && !this.CanResearch(template.pair))
-		return false;
-	
 	return this.CheckTechnologyRequirements(template.requirements);
 };
 
@@ -326,9 +341,9 @@
 }
 
 // Marks a technology as being currently researched
-TechnologyManager.prototype.StartedResearch = function (tech)
+TechnologyManager.prototype.StartedResearch = function (tech, researcher)
 {
-	this.inProgressTechs[tech] = true;
+	this.inProgressTechs[tech] = researcher;
 };
 
 // Marks a technology as not being currently researched
@@ -346,6 +361,14 @@
 		return false;
 };
 
+// Gets the entity currently researching a technology
+TechnologyManager.prototype.GetResearcher = function(tech)
+{
+	if (this.inProgressTechs[tech])
+		return this.inProgressTechs[tech];
+	return undefined;
+};
+
 // Get helper data for tech modifications
 TechnologyManager.prototype.GetTechModifications = function()
 {