diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/FlowDebugger.razor b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/FlowDebugger.razor
index 1809db49..67469b3c 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/FlowDebugger.razor
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/FlowDebugger.razor
@@ -235,7 +235,12 @@
                             else
                             {
                                 <div data-test="flow-script-params">
-                                    <ParameterValueForm ParameterDefinitions="@script.ParameterDefinitions"
+                                    @* Keyed on the script so a change of script REMOUNTS the form: its raw
+                                       text and parse errors are per-instance state that must not survive
+                                       (and two scripts may even declare byte-identical definitions, which
+                                       would otherwise skip the reparse and its ValidChanged entirely). *@
+                                    <ParameterValueForm @key="@script.CanonicalName"
+                                                        ParameterDefinitions="@script.ParameterDefinitions"
                                                         Values="_scriptParams"
                                                         ValuesChanged="@(v => _scriptParams = v)"
                                                         ValidChanged="@(ok => _scriptParamsValid = ok)" />
diff --git a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/FlowDebugger.razor.cs b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/FlowDebugger.razor.cs
index ccacf1a1..b61cf3d0 100644
--- a/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/FlowDebugger.razor.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/FlowDebugger.razor.cs
@@ -330,6 +330,11 @@ public partial class FlowDebugger : ComponentBase, IDisposable
         ResetResult();
         _predicted = null;
         _state = FlowState.Idle;
+        // Inputs are per-entry-point, as in OnScriptChangedAsync: never carry a script's value or
+        // parameter tree (or its validity) across a switch of entry kind.
+        _scriptParams = new();
+        _scriptParamsValid = false;
+        _valueChangeValue = string.Empty;
         await PersistAsync(StorageEntry, entry.ToString());
         if (_entry == EntryKind.Method && _selectedMethodId > 0)
             await OnMethodChangedAsync();
diff --git a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/FlowDebuggerPageTests.cs b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/FlowDebuggerPageTests.cs
index 56569c73..ccc22fea 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/FlowDebuggerPageTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/FlowDebuggerPageTests.cs
@@ -691,4 +691,64 @@ public class FlowDebuggerPageTests : BunitContext
         cut.WaitForAssertion(() => Assert.Equal("Manual", cut.Find("select[data-test='flow-script-select']").GetAttribute("value")));
         _ = _flow.Received().PredictScriptAsync(7, "Manual", Arg.Any<CancellationToken>());
     }
+
+    /// <summary>
+    /// Two call-kind scripts declaring BYTE-IDENTICAL parameter definitions — the case that makes
+    /// <c>ParameterValueForm</c> skip its reparse (and its <c>ValidChanged</c>) and keeps the previous
+    /// script's raw text and parse errors. The page must remount the form per script instead.
+    /// </summary>
+    private static readonly FlowScriptOption Manual2 = new("Manual2", "Call", null,
+        """{"type":"object","properties":{"n":{"type":"integer"}},"required":["n"]}""", 20);
+
+    private void WireInstanceWithTwinScripts()
+    {
+        _templates.GetInstancesBySiteIdAsync(1, Arg.Any<CancellationToken>())
+            .Returns(Task.FromResult<IReadOnlyList<Instance>>([new Instance("Sim01") { Id = 7, SiteId = 1, TemplateId = 10 }]));
+        _flow.GetInstanceScriptsAsync(7, Arg.Any<CancellationToken>())
+            .Returns(Task.FromResult<IReadOnlyList<FlowScriptOption>>([Manual, Manual2, Tick]));
+        _flow.PredictScriptAsync(7, Arg.Any<string>(), Arg.Any<CancellationToken>()).Returns(ThreeNodePrediction());
+    }
+
+    private IRenderedComponent<FlowDebuggerPage> ChooseScriptWithAnInvalidParameter()
+    {
+        var cut = Render<FlowDebuggerPage>();
+        cut.Find("button[data-test='flow-entry-script']").Click();
+        cut.Find("select[data-test='flow-site-select']").Change("1");
+        cut.Find("select[data-test='flow-instance-select']").Change("7");
+        cut.Find("select[data-test='flow-script-select']").Change("Manual");
+        cut.Find("#param-n").Input("abc"); // not an integer: the form parks a parse error
+        Assert.True(cut.Find("button[data-test='flow-run']").HasAttribute("disabled"));
+        return cut;
+    }
+
+    [Fact]
+    public void ScriptEntry_SwitchingBetweenCallKindScripts_ResetsTheFormAndValidity()
+    {
+        RegisterServices();
+        WireInstanceWithTwinScripts();
+        var cut = ChooseScriptWithAnInvalidParameter();
+
+        cut.Find("select[data-test='flow-script-select']").Change("Manual2");
+
+        // A fresh form: no echo of the previous script's text, and no stale parse error keeping
+        // Run disabled invisibly — Run is disabled only because the required field is unset.
+        Assert.Equal(string.Empty, cut.Find("#param-n").GetAttribute("value"));
+        Assert.True(cut.Find("button[data-test='flow-run']").HasAttribute("disabled"));
+
+        cut.Find("#param-n").Input("5");
+        Assert.False(cut.Find("button[data-test='flow-run']").HasAttribute("disabled"));
+    }
+
+    [Fact]
+    public void ScriptEntry_SwitchingFromAnInvalidFormToANoParameterScript_EnablesRun()
+    {
+        RegisterServices();
+        WireInstanceWithTwinScripts();
+        var cut = ChooseScriptWithAnInvalidParameter();
+
+        cut.Find("select[data-test='flow-script-select']").Change("Tick");
+
+        Assert.Contains("takes no parameters", cut.Find("[data-test='flow-inputs']").TextContent);
+        Assert.False(cut.Find("button[data-test='flow-run']").HasAttribute("disabled"));
+    }
 }