diff --git a/tvbwidgets/tests/test_head_widget.py b/tvbwidgets/tests/test_head_widget.py
index 232f856..8b2976a 100644
--- a/tvbwidgets/tests/test_head_widget.py
+++ b/tvbwidgets/tests/test_head_widget.py
@@ -126,3 +126,24 @@ def mockk(token):
 
     widget.load_selected_file(Sensors, '.txt')
     assert 'Could not load' in widget.message_label.value
+
+
+def test_head_widget_title_renders_class_name(mocker):
+    mocker.patch('k3d.Plot.display', lambda self: None)
+    widget = api.HeadWidget([])
+    html_widget = widget.children[0]
+    assert 'HeadWidget' in html_widget.value
+    assert "<class" not in html_widget.value, (
+        "HeadWidget title is rendering the class object. "
+        "Use HeadWidget.__name__ in the f-string, not HeadWidget directly."
+    )
+
+
+def test_head_widget_accepts_extra_kwargs(mocker):
+    mocker.patch('k3d.Plot.display', lambda self: None)
+    try:
+        widget = api.HeadWidget([], description="test")
+    except TypeError as e:
+        raise AssertionError(
+            f"HeadWidget crashed with extra kwargs — likely *kwargs instead of **kwargs: {e}"
+        )
diff --git a/tvbwidgets/tests/test_spacetime_widget.py b/tvbwidgets/tests/test_spacetime_widget.py
index 8e0827d..274ba88 100644
--- a/tvbwidgets/tests/test_spacetime_widget.py
+++ b/tvbwidgets/tests/test_spacetime_widget.py
@@ -76,8 +76,9 @@ def test_add_options(wid):
     assert wid.options.children[3].value == "None"
 
 
-
-
-    
-
-
+def test_default_border_not_mutated(wid):
+    from tvbwidgets.ui.base_widget import TVBWidget
+    assert 'min_width' not in TVBWidget.DEFAULT_BORDER, (
+        "SpaceTimeVisualizerWidget mutated the shared TVBWidget.DEFAULT_BORDER. "
+        "Use layout = {**self.DEFAULT_BORDER} instead of layout = self.DEFAULT_BORDER."
+    )
diff --git a/tvbwidgets/ui/head_widget.py b/tvbwidgets/ui/head_widget.py
index 329928b..840b0dd 100644
--- a/tvbwidgets/ui/head_widget.py
+++ b/tvbwidgets/ui/head_widget.py
@@ -57,8 +57,8 @@ def __init__(self, datatypes, width=1200, height=550, **kwargs):
         Docs
         """
         self.output = ipywidgets.Output(layout=ipywidgets.Layout(width=str(width) + 'px', height=str(height) + 'px'))
-        super(HeadWidget, self).__init__([ipywidgets.HTML(value=f'<h1>{HeadWidget}</h1>'), self.output],
-                                         layout=self.DEFAULT_BORDER, *kwargs)
+        super(HeadWidget, self).__init__([ipywidgets.HTML(value=f'<h1>{HeadWidget.__name__}</h1>'), self.output],
+                                         layout=self.DEFAULT_BORDER, **kwargs)
         self.plot = None
         self.refresh_plot(datatypes)
 
diff --git a/tvbwidgets/ui/spacetime_widget.py b/tvbwidgets/ui/spacetime_widget.py
index 189df4b..e64f9d7 100644
--- a/tvbwidgets/ui/spacetime_widget.py
+++ b/tvbwidgets/ui/spacetime_widget.py
@@ -272,7 +272,7 @@ def _create_plots_overview(self):
         plt.close(self.fig)
 
     def _prepare_plot_details(self):
-        layout = self.DEFAULT_BORDER
+        layout = {**self.DEFAULT_BORDER}
         layout['min_width'] = "150px"
         self.plot_details = HTML(
             value=self._generate_details(),