Index: /CKEditor/trunk/CHANGES.html
===================================================================
--- /CKEditor/trunk/CHANGES.html	(revision 6564)
+++ /CKEditor/trunk/CHANGES.html	(revision 6565)
@@ -80,4 +80,5 @@
 		<li><a href="http://dev.ckeditor.com/ticket/6849">#6849</a> : Correct enter key behavior on list item.</li>
 		<li><a href="http://dev.ckeditor.com/ticket/7113">#7113</a> : [Webkit]Undesired document scroll on click after scrolling.</li>
+		<li><a href="http://dev.ckeditor.com/ticket/6491">#6491</a> : Undesired image dialog dimension lock reset on url change.</li>
 		<li>Updated the following language files:<ul>
 			<li><a href="http://dev.ckeditor.com/ticket/7124">#7124</a> : Czech;</li>
Index: /CKEditor/trunk/_source/plugins/image/dialogs/image.js
===================================================================
--- /CKEditor/trunk/_source/plugins/image/dialogs/image.js	(revision 6564)
+++ /CKEditor/trunk/_source/plugins/image/dialogs/image.js	(revision 6565)
@@ -122,9 +122,8 @@
 				return null;
 
-			var ratioButton = CKEDITOR.document.getById( btnLockSizesId );
-
-			if ( oImageOriginal.getCustomData( 'isReady' ) == 'true' )
+			// Check image ratio and original image ratio, but respecting user's preference.
+			if ( value == 'check' )
 			{
-				if ( value == 'check' )			// Check image ratio and original image ratio.
+				if ( !dialog.userlockRatio && oImageOriginal.getCustomData( 'isReady' ) == 'true'  )
 				{
 					var width = dialog.getValueOf( 'info', 'txtWidth' ),
@@ -142,12 +141,14 @@
 					}
 				}
-				else if ( value != undefined )
-					dialog.lockRatio = value;
-				else
-					dialog.lockRatio = !dialog.lockRatio;
 			}
-			else if ( value != 'check' )		// I can't lock ratio if ratio is unknown.
-				dialog.lockRatio = false;
-
+			else if ( value != undefined )
+				dialog.lockRatio = value;
+			else
+			{
+				dialog.userlockRatio = 1;
+				dialog.lockRatio = !dialog.lockRatio;
+			}
+
+			var ratioButton = CKEDITOR.document.getById( btnLockSizesId );
 			if ( dialog.lockRatio )
 				ratioButton.removeClass( 'cke_btn_unlocked' );
@@ -276,4 +277,5 @@
 
 				this.lockRatio = true;
+				this.userlockRatio = 0;
 				this.dontResetSize = false;
 				this.firstLoad = true;
@@ -336,10 +338,10 @@
 					// Fill out all fields.
 					this.setupContent( IMAGE, this.imageElement );
-
-					// Refresh LockRatio button
-					switchLockRatio ( this, true );
 				}
 				else
 					this.imageElement =  editor.document.createElement( 'img' );
+
+				// Refresh LockRatio button
+				switchLockRatio ( this, true );
 
 				// Dont show preview if no URL given.