diff --git a/components/tachart/tacustomsource.pas b/components/tachart/tacustomsource.pas
index d68e0ac247..d229c2c9e9 100644
--- a/components/tachart/tacustomsource.pas
+++ b/components/tachart/tacustomsource.pas
@@ -849,7 +849,8 @@ begin
     end;
   end;
 
-  FBasicExtentIsValid := true;
+  FBasicExtentIsValid := not IsUpdating;  // When updating, we are not allowed
+    // to set "Valid" for caches - see comment in TListChartSource.ClearCaches()
   Result := FBasicExtent;
 end;
 
@@ -888,7 +889,8 @@ begin
               UpdateMinMax(XList[j], FXListExtent.a.X, FXListExtent.b.X);
         end;
 
-      FXListExtentIsValid := true;
+      FXListExtentIsValid := not IsUpdating;  // When updating, we are not allowed
+        // to set "Valid" for caches - see comment in TListChartSource.ClearCaches()
     end;
 
     Result.a.X := Min(Result.a.X, FXListExtent.a.X);
@@ -915,7 +917,8 @@ begin
               UpdateMinMax(YList[j], FYListExtent.a.Y, FYListExtent.b.Y);
         end;
 
-      FYListExtentIsValid := true;
+      FYListExtentIsValid := not IsUpdating;  // When updating, we are not allowed
+        // to set "Valid" for caches - see comment in TListChartSource.ClearCaches()
     end;
 
     Result.a.Y := Min(Result.a.Y, FYListExtent.a.Y);
@@ -1018,7 +1021,8 @@ begin
             end;
         end;
 
-      FCumulativeExtentIsValid := true;
+      FCumulativeExtentIsValid := not IsUpdating;  // When updating, we are not allowed
+        // to set "Valid" for caches - see comment in TListChartSource.ClearCaches()
     end;
 
     Result.a.Y := Min(Result.a.Y, FCumulativeExtent.a.Y);
@@ -1499,7 +1503,8 @@ begin
   for i := 0 to Count - 1 do
     with Item[i]^ do
       FValuesTotal += NumberOr(Y);
-  FValuesTotalIsValid := true;
+  FValuesTotalIsValid := not IsUpdating;  // When updating, we are not allowed
+    // to set "Valid" for caches - see comment in TListChartSource.ClearCaches()
   Result := FValuesTotal;
 end;
 
diff --git a/components/tachart/tasources.pas b/components/tachart/tasources.pas
index dbc29d4f99..483ec6d69b 100644
--- a/components/tachart/tasources.pas
+++ b/components/tachart/tasources.pas
@@ -720,16 +720,20 @@ end;
 
 procedure TListChartSource.ClearCaches;
 begin
+  // When updating, we are not allowed to set "Valid" for caches - cached
+  // data is not synchronized with real data when updating, so setting "Valid"
+  // could lead to reading outdated cache contents, when calling methods like
+  // BasicExtent() when still in update mode
   FBasicExtent := EmptyExtent;
-  FBasicExtentIsValid := true;
+  FBasicExtentIsValid := not IsUpdating;
   FCumulativeExtent := EmptyExtent;
-  FCumulativeExtentIsValid := true;
+  FCumulativeExtentIsValid := not IsUpdating;
   FXListExtent := EmptyExtent;
-  FXListExtentIsValid := true;
+  FXListExtentIsValid := not IsUpdating;
   FYListExtent := EmptyExtent;
-  FYListExtentIsValid := true;
+  FYListExtentIsValid := not IsUpdating;
   FValuesTotal := 0;
-  FValuesTotalIsValid := true;
+  FValuesTotalIsValid := not IsUpdating;
 end;
 
 procedure TListChartSource.CopyFrom(ASource: TCustomChartSource);