From bd2ae70ee9a8b4484956b819c0a1ee026e0be576 Mon Sep 17 00:00:00 2001
From: Peter Chapman <peter@conglomo.co.nz>
Date: Thu, 11 Dec 2025 07:43:52 +1300
Subject: [PATCH] Do not reset chapter one when it contains duplicate id tags

---
 .../Corpora/UpdateUsfmParserHandler.cs        |  9 ++--
 .../Corpora/UpdateUsfmParserHandlerTests.cs   | 45 +++++++++++++++++++
 2 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/src/SIL.Machine/Corpora/UpdateUsfmParserHandler.cs b/src/SIL.Machine/Corpora/UpdateUsfmParserHandler.cs
index d6a23618..00c1f719 100644
--- a/src/SIL.Machine/Corpora/UpdateUsfmParserHandler.cs
+++ b/src/SIL.Machine/Corpora/UpdateUsfmParserHandler.cs
@@ -124,9 +124,12 @@ public override void EndUsfm(UsfmParserState state)
 
         public override void StartBook(UsfmParserState state, string marker, string code)
         {
-            _verseRowsRef = state.VerseRef;
-            UpdateVerseRowsMap();
-            UpdateVerseRows();
+            if (_verseRowsRef.BookNum != state.VerseRef.BookNum)
+            {
+                _verseRowsRef = state.VerseRef;
+                UpdateVerseRowsMap();
+                UpdateVerseRows();
+            }
 
             CollectReadonlyTokens(state);
             _updateBlocks.Push(new UsfmUpdateBlock());
diff --git a/tests/SIL.Machine.Tests/Corpora/UpdateUsfmParserHandlerTests.cs b/tests/SIL.Machine.Tests/Corpora/UpdateUsfmParserHandlerTests.cs
index 98d67f4e..77c9f7cc 100644
--- a/tests/SIL.Machine.Tests/Corpora/UpdateUsfmParserHandlerTests.cs
+++ b/tests/SIL.Machine.Tests/Corpora/UpdateUsfmParserHandlerTests.cs
@@ -1306,6 +1306,51 @@ public void GetUsfm_DuplicateVerses()
         AssertUsfmEquals(target, resultP);
     }
 
+    [Test]
+    public void GetUsfm_IdTags()
+    {
+        var rows = new List<UpdateUsfmRow>
+        {
+            new UpdateUsfmRow(ScrRef("MAT 1:0/1:s"), "new section header"),
+            new UpdateUsfmRow(ScrRef("MAT 1:1"), "new verse 1"),
+            new UpdateUsfmRow(ScrRef("MAT 1:2"), "new verse 2"),
+            new UpdateUsfmRow(ScrRef("MAT 1:3"), "new verse 3"),
+            new UpdateUsfmRow(ScrRef("MAT 1:4"), "new verse 4"),
+        };
+
+        string usfm =
+            @"\id MAT
+\s section header
+\c 1
+\s1 beginning-of-chapter header
+\p
+\v 1 verse 1
+\id
+\v 2 verse 2
+\id MAT
+\v 3 verse 3
+\id MRK
+\v 4 verse 4
+";
+
+        string target = UpdateUsfm(rows, usfm, paragraphBehavior: UpdateUsfmMarkerBehavior.Strip);
+        string resultP =
+            @"\id MAT
+\s new section header
+\c 1
+\s1 beginning-of-chapter header
+\p
+\v 1 new verse 1
+\id
+\v 2 new verse 2
+\id MAT
+\v 3 new verse 3
+\id MRK
+\v 4 new verse 4
+";
+        AssertUsfmEquals(target, resultP);
+    }
+
     [Test]
     public void GetUsfm_PreferExisting_AddRemark()
     {