Only need to force removal of conditional attribute bindings

pkg/mdv/lib/src/element.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of mdv;
 
 /** Extensions to the [Element] API. */
 class _ElementExtension extends _NodeExtension {
   _ElementExtension(Element node) : super(node);
 
   Element get node => super.node;
 
   Map<String, StreamSubscription> _attributeBindings;
 
   // TODO(jmesserly): should path be optional, and default to empty path?
   // It is used that way in at least one path in JS TemplateElement tests
   // (see "BindImperative" test in original JS code).
   void bind(String name, model, String path) {
     if (_attributeBindings == null) {
       _attributeBindings = new Map<String, StreamSubscription>();
     }
 
-    node.xtag.attributes.remove(name);
-
     var changed;
     if (name.endsWith('?')) {
+      node.xtag.attributes.remove(name);
       name = name.substring(0, name.length - 1);
 
       changed = (value) {
         if (_toBoolean(value)) {
           node.xtag.attributes[name] = '';
         } else {
           node.xtag.attributes.remove(name);
         }
       };
     } else {
@@ skipping 18 matching lines @@
 
   void unbindAll() {
     if (_attributeBindings != null) {
       for (var binding in _attributeBindings.values) {
         binding.cancel();
       }
       _attributeBindings = null;
     }
   }
 }