diff --git a/zxlive/custom_rule.py b/zxlive/custom_rule.py
index 14f68e7..5bffb15 100644
--- a/zxlive/custom_rule.py
+++ b/zxlive/custom_rule.py
@@ -266,11 +266,8 @@ def filter_matchings_if_symbolic_compatible(matchings: list[Dict[VT, VT]], left:
     for matching in matchings:
         if len(matching) != len(left):
             continue
-        try:
-            match_symbolic_parameters(matching, left, right)
-            new_matchings.append(matching)
-        except ValueError:
-            pass
+        match_symbolic_parameters(matching, left, right)
+        new_matchings.append(matching)
     return new_matchings
 
 
diff --git a/zxlive/dialogs.py b/zxlive/dialogs.py
index 81bca9b..d069f5f 100644
--- a/zxlive/dialogs.py
+++ b/zxlive/dialogs.py
@@ -210,10 +210,7 @@ def save_diagram_dialog(graph: GraphT, parent: QWidget) -> Optional[tuple[str, F
     file_path, selected_format = file_path_and_format
 
     if selected_format in (FileFormat.QGraph, FileFormat.Json):
-        try:
-            graph.auto_detect_io()
-        except TypeError:
-            pass
+        graph.auto_detect_io()
         data = graph.to_json()
     elif selected_format == FileFormat.QASM:
         try:
diff --git a/zxlive/rewrite_action.py b/zxlive/rewrite_action.py
index 4ca0c0d..5d359f6 100644
--- a/zxlive/rewrite_action.py
+++ b/zxlive/rewrite_action.py
@@ -112,6 +112,8 @@ def do_rewrite(self, panel: ProofPanel) -> None:
 
         try:
             g, rem_verts = self.apply_rewrite(g, matches)
+        except ValueError as ex:
+            raise ex
         except Exception as ex:
             show_error_msg('Error while applying rewrite rule', str(ex))
             return
diff --git a/zxlive/rule_panel.py b/zxlive/rule_panel.py
index dbc4cd6..d950dde 100644
--- a/zxlive/rule_panel.py
+++ b/zxlive/rule_panel.py
@@ -96,12 +96,9 @@ def add_edge(self, u: VT, v: VT) -> None:
         self.update_io_labels(self.graph_scene)
 
     def update_io_labels(self, scene: EditGraphScene) -> None:
-        try:
-            scene.g.auto_detect_io()
-            for v in scene.g.vertices():
-                if v in scene.g.inputs():
-                    scene.vertex_map[v].phase_item.setPlainText("in-" + str(scene.g.inputs().index(v)))
-                elif v in scene.g.outputs():
-                    scene.vertex_map[v].phase_item.setPlainText("out-" + str(scene.g.outputs().index(v)))
-        except TypeError:
-            return
+        scene.g.auto_detect_io()
+        for v in scene.g.vertices():
+            if v in scene.g.inputs():
+                scene.vertex_map[v].phase_item.setPlainText("in-" + str(scene.g.inputs().index(v)))
+            elif v in scene.g.outputs():
+                scene.vertex_map[v].phase_item.setPlainText("out-" + str(scene.g.outputs().index(v)))
diff --git a/zxlive/vitem.py b/zxlive/vitem.py
index 8e386be..e704757 100644
--- a/zxlive/vitem.py
+++ b/zxlive/vitem.py
@@ -107,6 +107,7 @@ def g(self) -> GraphT:
 
     @property
     def ty(self) -> VertexType:
+        # https://github.com/zxcalc/zxlive/pull/281
         _ty: VertexType = self.g.type(self.v)
         return _ty