Index: trac/ticket/api.py
===================================================================
--- trac/ticket/api.py	(revision 10642)
+++ trac/ticket/api.py	(working copy)
@@ -211,7 +211,7 @@
     default_keywords = Option('ticket', 'default_keywords', '',
         """Default keywords for newly created tickets.""")
 
-    default_owner = Option('ticket', 'default_owner', '',
+    default_owner = Option('ticket', 'default_owner', '< default >',
         """Default owner for newly created tickets.""")
 
     default_cc = Option('ticket', 'default_cc', '',
@@ -408,6 +408,7 @@
                                                            ticket.resource):
                     possible_owners.append(user)
             possible_owners.sort()
+            possible_owners.insert(0, '< default >')
             field['options'] = possible_owners
             field['optional'] = True
 
Index: trac/ticket/model.py
===================================================================
--- trac/ticket/model.py	(revision 10642)
+++ trac/ticket/model.py	(working copy)
@@ -200,14 +200,18 @@
         self.values['time'] = self.values['changetime'] = when
 
         # The owner field defaults to the component owner
-        if self.values.get('component') and not self.values.get('owner'):
-            try:
-                component = Component(self.env, self['component'])
-                if component.owner:
-                    self['owner'] = component.owner
-            except ResourceNotFound:
-                # No such component exists
-                pass
+        if self.values.get('owner') == '< default >':
+            default_to_owner = ''
+            if self.values.get('component'):
+                try:
+                    component = Component(self.env, self['component'])
+                    default_to_owner = component.owner # even if it's empty
+                except ResourceNotFound:
+                    # No such component exists
+                    pass
+            # If the current owner is "< default >", we need to set it to
+            # _something_ else, even if that something else is blank.
+            self['owner'] = default_to_owner
 
         # Perform type conversions
         values = dict(self.values)