diff --git a/docs/configuration_reference/behavior_version.rst b/docs/configuration_reference/behavior_version.rst
index 60c30d016b..af8a270ac0 100644
--- a/docs/configuration_reference/behavior_version.rst
+++ b/docs/configuration_reference/behavior_version.rst
@@ -22,6 +22,15 @@ and not listing legacy/deprecated parameters.
 Version History
 ---------------
 
+Behavior version 11 (2021-12-16)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Broadcasting dims no longer match in :class:`CombineLayer` and others.
+This was never needed, instead broadcasting happens in RETURNN automatically to non-existing dims.
+To fix this, do not add any broadcasting dims.
+
+See issue `#666 <https://github.com/rwth-i6/returnn/issues/666>`__.
+
 Behavior version 10 (2021-12-07)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/returnn/tf/layers/basic.py b/returnn/tf/layers/basic.py
index 7839a4730f..f83ce8e032 100644
--- a/returnn/tf/layers/basic.py
+++ b/returnn/tf/layers/basic.py
@@ -1282,7 +1282,10 @@ def _get_common_input_position_axes(cls, input_data, position_data, old_gather_a
     :return: (common_axes_input, common_axes_position, specific_input_axes, specific_position_axes), all counted with
     batch dim.
     """
-    is_equal_opts = dict(allow_same_spatial_dim=True, broadcast_matches=True)
+    from returnn.util import BehaviorVersion
+    is_equal_opts = dict(allow_same_spatial_dim=True)
+    if BehaviorVersion.get() < 11:
+      is_equal_opts["broadcast_matches"] = True
     all_dim_tags, tags_dict = Dim.get_all_dimension_tags([input_data, position_data], is_equal_opts=is_equal_opts)
     input_tags, pos_tags = tags_dict[input_data], tags_dict[position_data]
     specific_input_axes = [i for i, tag in enumerate(input_tags) if tag not in pos_tags and i != old_gather_axis]
@@ -6420,9 +6423,12 @@ def _auto_var_axes(source1, source2, red1, red2):
     :return: var1 tags, var2 tags
     :rtype: (list[Dim], list[Dim])
     """
+    from returnn.util import BehaviorVersion
     is_equal_opts = dict(
       treat_feature_as_spatial=True, allow_same_spatial_dim=True,
-      broadcast_matches=True, undefined_matches=True, derived_matches=True)
+      undefined_matches=True, derived_matches=True)
+    if BehaviorVersion.get() < 11:
+      is_equal_opts["broadcast_matches"] = True
     all_dim_tags, tags_dict = Dim.get_all_dimension_tags([source1, source2], is_equal_opts=is_equal_opts)
     tags1, tags2 = tags_dict[source1], tags_dict[source2]
     var1 = [tag for i, tag in enumerate(tags1) if tag not in tags2 and i not in red1]
diff --git a/returnn/tf/util/data.py b/returnn/tf/util/data.py
index 869093ba9b..74a1c08a42 100644
--- a/returnn/tf/util/data.py
+++ b/returnn/tf/util/data.py
@@ -5049,6 +5049,7 @@ def get_common_data(cls, sources, ignore_feature_dim=False, allow_broadcast_all_
       This is always a template, and a new copy.
     :rtype: Data|None
     """
+    from returnn.util import BehaviorVersion
     if not sources:
       return None
     assert sources
@@ -5067,8 +5068,10 @@ def get_common_data(cls, sources, ignore_feature_dim=False, allow_broadcast_all_
       common.beam = SearchBeam.get_combined_beam(*[s.beam for s in sources])
     is_equal_opts = dict(
       ignore_feature_dim=ignore_feature_dim, treat_feature_as_spatial=True,
-      allow_same_spatial_dim=True, broadcast_matches=True,
+      allow_same_spatial_dim=True,
       undefined_matches=True, derived_matches=True)
+    if BehaviorVersion.get() < 11:
+      is_equal_opts["broadcast_matches"] = True
     all_dim_tags, tags_dict = Dim.get_all_dimension_tags(sources, is_equal_opts=is_equal_opts)
     # Check for potential undefined tags, and replace those with defined tags if possible.
     for axis, dim_tag in enumerate(common.dim_tags):
diff --git a/returnn/util/basic.py b/returnn/util/basic.py
index e7270d1fdf..c09e41f42b 100644
--- a/returnn/util/basic.py
+++ b/returnn/util/basic.py
@@ -209,7 +209,7 @@ class BehaviorVersion:
   The version will be set after the config is defined at __main__.init_config() or Engine.__init__()
   """
 
-  _latest_behavior_version = 10
+  _latest_behavior_version = 11
   _behavior_version = None  # type: typing.Optional[int]
 
   @classmethod