diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index 52a3affa81a9..23173847b200 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -4433,12 +4433,14 @@ def check_op(
                 recent_context.line = err.line
                 recent_context.column = err.column
                 if len(left_variants) >= 2 and len(right_variants) >= 2:
-                    self.msg.warn_both_operands_are_from_unions(recent_context)
+                    self.msg.warn_both_operands_are_from_unions(recent_context, parent_error=err)
                 elif len(left_variants) >= 2:
-                    self.msg.warn_operand_was_from_union("Left", base_type, context=recent_context)
+                    self.msg.warn_operand_was_from_union(
+                        "Left", base_type, context=recent_context, parent_error=err
+                    )
                 elif len(right_variants) >= 2:
                     self.msg.warn_operand_was_from_union(
-                        "Right", right_type, context=recent_context
+                        "Right", right_type, context=recent_context, parent_error=err
                     )
 
             # See the comment in 'check_overload_call' for more details on why
diff --git a/mypy/errors.py b/mypy/errors.py
index e95904ce355e..6a37f7048209 100644
--- a/mypy/errors.py
+++ b/mypy/errors.py
@@ -149,7 +149,7 @@ def __init__(
         self.code = code
         self.blocker = blocker
         self.only_once = only_once
-        self.origin_span = origin_span or [line]
+        self.origin_span = list(origin_span) if origin_span is not None else [line]
         self.target = target
         self.priority = priority
         if parent_error is not None:
@@ -776,6 +776,15 @@ def add_error_info(self, info: ErrorInfo, *, file: str | None = None) -> None:
         if self._filter_error(file, info):
             return
         if not info.blocker:  # Blockers cannot be ignored
+            if info.parent_error is not None and file in self.ignored_lines:
+                # A note attached to an error must not outlive its parent: if
+                # the parent error is ignored on its own line(s), the note is
+                # not shown even if it is reported on another line.
+                for scope_line in info.parent_error.origin_span:
+                    if self.is_ignored_error(
+                        scope_line, info.parent_error, self.ignored_lines[file]
+                    ):
+                        return
             if file in self.ignored_lines:
                 # Check each line in this context for "type: ignore" comments.
                 # line == end_line for most nodes, so we only loop once.
diff --git a/mypy/messages.py b/mypy/messages.py
index 0f3a5be368a4..3bfb3c79cbd2 100644
--- a/mypy/messages.py
+++ b/mypy/messages.py
@@ -1775,14 +1775,24 @@ def overloaded_signatures_ret_specific(self, index: int, context: Context) -> No
             context,
         )
 
-    def warn_both_operands_are_from_unions(self, context: Context) -> None:
-        self.note("Both left and right operands are unions", context, code=codes.OPERATOR)
+    def warn_both_operands_are_from_unions(
+        self, context: Context, parent_error: ErrorInfo | None = None
+    ) -> None:
+        self.note(
+            "Both left and right operands are unions",
+            context,
+            code=codes.OPERATOR,
+            parent_error=parent_error,
+        )
 
-    def warn_operand_was_from_union(self, side: str, original: Type, context: Context) -> None:
+    def warn_operand_was_from_union(
+        self, side: str, original: Type, context: Context, parent_error: ErrorInfo | None = None
+    ) -> None:
         self.note(
             f"{side} operand is of type {format_type(original, self.options)}",
             context,
             code=codes.OPERATOR,
+            parent_error=parent_error,
         )
 
     def operator_method_signatures_overlap(
diff --git a/test-data/unit/check-unions.test b/test-data/unit/check-unions.test
index 6394e0722501..3975120d4c04 100644
--- a/test-data/unit/check-unions.test
+++ b/test-data/unit/check-unions.test
@@ -109,6 +109,16 @@ x[2] + 1 # E: Unsupported operand types for + ("str" and "int") \
          # N: Left operand is of type "int | str"
 [builtins fixtures/isinstancelist.pyi]
 
+[case testIgnoredOperatorErrorDoesNotLeakNote]
+# A note attached to an error ignored by a "type: ignore" comment on a
+# different line of the same multi-line expression must not leak.
+a:b
+b =dict[0, b|0]  # type:ignore[valid-type]
+a[0
+]+"" # type:ignore[operator]
+[builtins fixtures/isinstancelist.pyi]
+
+
 [case testUnionAsOverloadArg]
 from foo import *
 x = 0