diff --git a/content/treestyletab/treestyletab.js b/content/treestyletab/treestyletab.js
index c8af2744..0f758c02 100644
--- a/content/treestyletab/treestyletab.js
+++ b/content/treestyletab/treestyletab.js
@@ -1407,7 +1407,6 @@ var TreeStyleTabService = {
 								aEvent.screenX - box.screenX,
 								aEvent.screenY - box.screenY
 							);
-							this.mPanelContainer.setAttribute(sv.kDROP_POSITION, sv.kDROP_POSITION_UNKNOWN);
 							aEvent.stopPropagation();
 						}
 						else $&]]>
diff --git a/content/treestyletab/treestyletabbrowser_tabbarDNDObserver.js b/content/treestyletab/treestyletabbrowser_tabbarDNDObserver.js
index 83d5efe5..1953db88 100644
--- a/content/treestyletab/treestyletabbrowser_tabbarDNDObserver.js
+++ b/content/treestyletab/treestyletabbrowser_tabbarDNDObserver.js
@@ -20,7 +20,6 @@ TreeStyleTabBrowserTabbarDNDObserver.prototype = {
 				sv.kTABBAR_MOVE_FORCE :
 				sv.kTABBAR_MOVE_NORMAL
 		);
-		sv.mTabBrowser.setAttribute(sv.kDROP_POSITION, sv.kDROP_POSITION_UNKNOWN);
 
 		aEvent.stopPropagation();
 		return true;
diff --git a/content/treestyletab/treestyletabbrowser_tabpanelDNDObserver.js b/content/treestyletab/treestyletabbrowser_tabpanelDNDObserver.js
index 0586b968..68093f58 100644
--- a/content/treestyletab/treestyletabbrowser_tabpanelDNDObserver.js
+++ b/content/treestyletab/treestyletabbrowser_tabpanelDNDObserver.js
@@ -9,7 +9,8 @@ TreeStyleTabBrowserTabpanelDNDObserver.prototype = {
 	{
 		if (!this.canDrop(aEvent, aDragSession)) return;
 		var sv = this.mOwner;
-		sv.mTabBrowser.setAttribute(sv.kDROP_POSITION, sv.kDROP_POSITION_UNKNOWN);
+		if (sv.mTabBrowser.hasAttribute(sv.kDROP_POSITION))
+			sv.mTabBrowser.setAttribute(sv.kDROP_POSITION, sv.kDROP_POSITION_UNKNOWN);
 	},
  
 	onDragOver : function(aEvent, aFlavour, aDragSession)