diff --git a/lektor_groupby/plugin.py b/lektor_groupby/plugin.py
index 9f92f9b..9a7a11d 100644
--- a/lektor_groupby/plugin.py
+++ b/lektor_groupby/plugin.py
@@ -1,9 +1,10 @@
 from lektor.builder import Builder  # typing
+from lektor.db import Page  # typing
 from lektor.pluginsystem import Plugin  # subclass
 from lektor.sourceobj import SourceObject  # typing
 
-from typing import List, Optional, Iterator
-from .vobj import GroupBySource, GroupByBuildProgram, VPATH
+from typing import List, Optional, Iterator, Any
+from .vobj import GroupBySource, GroupByBuildProgram, VPATH, VGroups
 from .groupby import GroupBy
 from .pruner import prune
 from .watcher import GroupByCallbackArgs  # typing
@@ -13,10 +14,10 @@ class GroupByPlugin(Plugin):
     name = 'GroupBy Plugin'
     description = 'Cluster arbitrary records with field attribute keyword.'
 
-    def on_setup_env(self, **extra: object) -> None:
+    def on_setup_env(self, **extra: Any) -> None:
         self.creator = GroupBy()
         self.env.add_build_program(GroupBySource, GroupByBuildProgram)
-        self.env.jinja_env.filters.update(vgroups=GroupBySource.of_record)
+        self.env.jinja_env.filters.update(vgroups=VGroups.iter)
 
         # resolve /tag/rss/ -> /tag/rss/index.html (local server only)
         @self.env.urlresolver
@@ -46,7 +47,7 @@ class GroupByPlugin(Plugin):
                 if isinstance(val, (list, map)):
                     yield from val
 
-    def on_before_build_all(self, builder: Builder, **extra: object) -> None:
+    def on_before_build_all(self, builder: Builder, **extra: Any) -> None:
         self.creator.clear_previous_results()
         self._load_quick_config()
         # let other plugins register their @groupby.watch functions
@@ -54,14 +55,15 @@ class GroupByPlugin(Plugin):
         self.config_dependencies = self.creator.get_dependencies()
         self.creator.make_cluster(builder)
 
-    def on_before_build(self, source: SourceObject, **extra: object) -> None:
+    def on_before_build(self, source: SourceObject, **extra: Any) -> None:
         # before-build may be called before before-build-all (issue #1017)
         # make sure it is evaluated immediatelly
-        self.creator.queue_now(source)
+        if isinstance(source, Page):
+            self.creator.queue_now(source)
 
-    def on_after_build_all(self, builder: Builder, **extra: object) -> None:
+    def on_after_build_all(self, builder: Builder, **extra: Any) -> None:
         self.creator.build_all(builder)
 
-    def on_after_prune(self, builder: Builder, **extra: object) -> None:
+    def on_after_prune(self, builder: Builder, **extra: Any) -> None:
         # TODO: find a better way to prune unreferenced elements
         prune(builder, VPATH)
diff --git a/lektor_groupby/vobj.py b/lektor_groupby/vobj.py
index 17f097f..02d97ff 100644
--- a/lektor_groupby/vobj.py
+++ b/lektor_groupby/vobj.py
@@ -51,7 +51,7 @@ class GroupBySource(VirtualSourceObject):
             if child.pad != record.pad:
                 child = record.pad.get(child.path)
             self._children[child] = extras
-        self._reverse_reference_records()
+            VGroups.of(child).add(self)
         # extra fields
         for attr, expr in config.fields.items():
             setattr(self, attr, self._eval(expr, field='fields.' + attr))
@@ -138,19 +138,23 @@ class GroupBySource(VirtualSourceObject):
         return '<GroupBySource path="{}" children={}>'.format(
             self.path, len(self._children))
 
-    # ---------------------
-    #   Reverse Reference
-    # ---------------------
 
-    def _reverse_reference_records(self) -> None:
-        ''' Attach self to page records. '''
-        for child in self._children:
-            if not hasattr(child, '_vgroups'):
-                child._vgroups = WeakSet()  # type: ignore[attr-defined]
-            child._vgroups.add(self)  # type: ignore[attr-defined]
+# -----------------------------------
+#          Reverse Reference
+# -----------------------------------
+
+class VGroups:
+    @staticmethod
+    def of(record: Record) -> WeakSet:
+        try:
+            wset = record.__vgroups  # type: ignore[attr-defined]
+        except AttributeError:
+            wset = WeakSet()
+            record.__vgroups = wset  # type: ignore[attr-defined]
+        return wset  # type: ignore[no-any-return]
 
     @staticmethod
-    def of_record(
+    def iter(
         record: Record,
         *keys: str,
         recursive: bool = False
@@ -167,9 +171,8 @@ class GroupBySource(VirtualSourceObject):
             page = proc_list.pop(0)
             if recursive and hasattr(page, 'children'):
                 proc_list.extend(page.children)  # type: ignore[attr-defined]
-            if not hasattr(page, '_vgroups'):
-                continue
-            for vobj in page._vgroups:  # type: ignore[attr-defined]
+            for vobj in VGroups.of(page):
+                vobj.config.dependencies
                 if not keys or vobj.config.key in keys:
                     yield vobj