Consider as loaded the fields marked as modified

As the load method skips setting modified fields, so they are not and will
never be marked as loaded.

sao/src/model.js

@@ -1355,17 +1355,13 @@
             }
         },
         get_loaded: function(fields) {
-            if (!jQuery.isEmptyObject(fields)) {
-                var result = true;
-                for (const field of fields) {
-                    if (!(field in this._loaded) && !(field in this.modified_fields)) {
-                        result = false;
-                    }
-                }
-                return result;
+            if (!fields) {
+                fields = Object.keys(this.model.fields);
             }
-            return Sao.common.compare(Object.keys(this.model.fields).sort(),
-                    Object.keys(this._loaded).sort());
+            fields = new Set(fields);
+            var loaded = new Set(Object.keys(this._loaded));
+            loaded = loaded.union(new Set(Object.keys(this.modified_fields)));
+            return fields.isSubsetOf(loaded);
         },
         get root_parent() {
             var parent = this;

sao/src/sao.js

@@ -136,6 +136,19 @@ var Sao = {
         }
     }
 
+    if (!Set.prototype.union) {
+        Set.prototype.union = function(other) {
+            if (this === null) {
+                throw new TypeError();
+            }
+            const result = new Set(this);
+            for (const key of other.keys()) {
+                result.add(key);
+            }
+            return result
+        }
+    }
+
     Sao.setdefault = function(object, key, value) {
         if (!Object.prototype.hasOwnProperty.call(object, key)) {
             object[key] = value;

tryton/tryton/gui/window/view_form/model/record.py

@@ -303,9 +303,9 @@ class Record:
             self.reload(fields)
 
     def get_loaded(self, fields=None):
-        if fields:
-            return set(fields) <= (self._loaded | set(self.modified_fields))
-        return set(self.group.fields.keys()) == self._loaded
+        if fields is None:
+            fields = self.group.fields.keys()
+        return set(fields) <= (self._loaded | set(self.modified_fields))
 
     loaded = property(get_loaded)