diff --git a/src/MxGateway.Worker.Tests/MxAccess/MxAccessEventMapperTests.cs b/src/MxGateway.Worker.Tests/MxAccess/MxAccessEventMapperTests.cs
index 0f2e524..5b48a31 100644
--- a/src/MxGateway.Worker.Tests/MxAccess/MxAccessEventMapperTests.cs
+++ b/src/MxGateway.Worker.Tests/MxAccess/MxAccessEventMapperTests.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Globalization;
 using MxGateway.Contracts.Proto;
 using MxGateway.Worker.MxAccess;
 
@@ -179,6 +180,63 @@ public sealed class MxAccessEventMapperTests
         Assert.Null(mxEvent.OnAlarmTransition.OriginalRaiseTimestamp);
     }
 
+    /// <summary>
+    ///     Verifies that an OnDataChange whose timestamp arrives as the
+    ///     VT_BSTR string MXAccess actually delivers still populates
+    ///     <see cref="MxEvent.SourceTimestamp"/> — the string is parsed as
+    ///     local time and converted to UTC.
+    /// </summary>
+    [Fact]
+    public void CreateOnDataChange_WithMxAccessStringTimestamp_SetsSourceTimestamp()
+    {
+        // The exact shape MXAccess fires (see captures/003-subscribe-scalars).
+        const string mxAccessTimestamp = "3/26/2026 1:38:22.907 PM";
+
+        MxEvent mxEvent = mapper.CreateOnDataChange(
+            "session-1",
+            serverHandle: 1,
+            itemHandle: 1,
+            value: 99,
+            quality: 192,
+            timestamp: mxAccessTimestamp,
+            statuses: null);
+
+        Assert.NotNull(mxEvent.SourceTimestamp);
+
+        DateTime localWall = new(2026, 3, 26, 13, 38, 22, 907, DateTimeKind.Unspecified);
+        DateTime expectedUtc = DateTime.SpecifyKind(localWall, DateTimeKind.Local).ToUniversalTime();
+        Assert.Equal(expectedUtc, mxEvent.SourceTimestamp.ToDateTime());
+    }
+
+    /// <summary>
+    ///     Verifies the MXAccess timestamp string is interpreted as the host's
+    ///     local time and returned as UTC. Written timezone-independently by
+    ///     round-tripping a local wall-clock time.
+    /// </summary>
+    [Fact]
+    public void TryParseSourceTimestamp_InterpretsStringAsLocalTime()
+    {
+        DateTime localWall = new(2026, 5, 21, 13, 43, 26, DateTimeKind.Unspecified);
+        string text = localWall.ToString(CultureInfo.CurrentCulture);
+
+        Assert.True(MxAccessEventMapper.TryParseSourceTimestamp(text, out DateTime utc));
+        Assert.Equal(DateTimeKind.Utc, utc.Kind);
+
+        DateTime expectedUtc = DateTime.SpecifyKind(localWall, DateTimeKind.Local).ToUniversalTime();
+        Assert.Equal(expectedUtc, utc);
+    }
+
+    /// <summary>Verifies unparseable or empty timestamp input is rejected without throwing.</summary>
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    [InlineData("not a timestamp")]
+    public void TryParseSourceTimestamp_RejectsUnparseableInput(string? text)
+    {
+        Assert.False(MxAccessEventMapper.TryParseSourceTimestamp(text, out _));
+    }
+
     private sealed class FakeStatus
     {
         public int success;
diff --git a/src/MxGateway.Worker/MxAccess/MxAccessEventMapper.cs b/src/MxGateway.Worker/MxAccess/MxAccessEventMapper.cs
index 6712020..585a651 100644
--- a/src/MxGateway.Worker/MxAccess/MxAccessEventMapper.cs
+++ b/src/MxGateway.Worker/MxAccess/MxAccessEventMapper.cs
@@ -1,4 +1,6 @@
 using System;
+using System.Globalization;
+using Google.Protobuf.WellKnownTypes;
 using MxGateway.Contracts.Proto;
 using MxGateway.Worker.Conversion;
 
@@ -265,6 +267,19 @@ public sealed class MxAccessEventMapper
             return;
         }
 
+        // MXAccess fires OnDataChange with pftItemTimeStamp marshaled as a
+        // VT_BSTR string (e.g. "3/26/2026 1:38:22.907 PM"), not a FILETIME or
+        // a VT_DATE — so the variant converter classifies it as a plain
+        // string and the timestamp would otherwise be dropped. Parse it here
+        // so the source timestamp still reaches MxEvent. MXAccess formats the
+        // string in the worker host's local time; see TryParseSourceTimestamp.
+        if (convertedTimestamp.KindCase == MxValue.KindOneofCase.StringValue
+            && TryParseSourceTimestamp(convertedTimestamp.StringValue, out DateTime parsedUtc))
+        {
+            mxEvent.SourceTimestamp = Timestamp.FromDateTime(parsedUtc);
+            return;
+        }
+
         if (!string.IsNullOrWhiteSpace(convertedTimestamp.RawDiagnostic))
         {
             mxEvent.RawStatus = string.IsNullOrWhiteSpace(mxEvent.RawStatus)
@@ -273,6 +288,38 @@ public sealed class MxAccessEventMapper
         }
     }
 
+    /// <summary>
+    ///     Parses an MXAccess <c>OnDataChange</c> timestamp string into a UTC
+    ///     <see cref="DateTime"/>. MXAccess delivers the value as a culture-
+    ///     formatted string rather than a FILETIME or VT_DATE, and formats it
+    ///     in the worker host's <em>local</em> time (verified empirically — a
+    ///     fast-changing tag's timestamp lands the host's UTC offset behind
+    ///     wall-clock UTC). The parsed value is therefore taken as local time
+    ///     and converted to UTC. Tries the worker host's culture first
+    ///     (MXAccess formats with the host locale), then the invariant culture.
+    /// </summary>
+    /// <param name="text">The MXAccess timestamp string.</param>
+    /// <param name="utc">The parsed UTC timestamp on success.</param>
+    /// <returns><see langword="true"/> when the string parsed successfully.</returns>
+    internal static bool TryParseSourceTimestamp(string? text, out DateTime utc)
+    {
+        utc = default;
+        if (string.IsNullOrWhiteSpace(text))
+        {
+            return false;
+        }
+
+        const DateTimeStyles styles = DateTimeStyles.AssumeLocal | DateTimeStyles.AdjustToUniversal;
+        if (DateTime.TryParse(text, CultureInfo.CurrentCulture, styles, out DateTime parsed)
+            || DateTime.TryParse(text, CultureInfo.InvariantCulture, styles, out parsed))
+        {
+            utc = DateTime.SpecifyKind(parsed, DateTimeKind.Utc);
+            return true;
+        }
+
+        return false;
+    }
+
     private MxArray ConvertBufferedArray(
         object? value,
         MxDataType expectedElementDataType)