More tweaks on when to disable source.

src/NTwain/Internals/ITwainSessionInternal.cs

@@ -46,6 +46,8 @@ namespace NTwain.Internals
 
         ReturnCode EnableSource(SourceEnableMode mode, bool modal, IntPtr windowHandle);
 
+        bool CloseDSRequested { get; }
+
         /// <summary>
         /// Gets the triplet operations defined for audio data group.
         /// </summary>

src/NTwain/Internals/TransferLogic.cs

@@ -58,7 +58,7 @@ namespace NTwain.Internals
 
                     #region actually handle xfer
 
-                    if (preXferArgs.CancelAll)
+                    if (preXferArgs.CancelAll || session.CloseDSRequested)
                     {
                         rc = session.DGControl.PendingXfers.Reset(pending);
                     }
@@ -99,21 +99,11 @@ namespace NTwain.Internals
                                 }
                             }
                         }
-
+                        
-
-                        switch (rc)
-                        {
-                            case ReturnCode.Cancel:
-                            default:
-                                // as usual
-                                rc = session.DGControl.PendingXfers.EndXfer(pending);
-                                break;
-                        }
-
                         if (rc != ReturnCode.Success && session.StopOnTransferError)
                         {
                             // end xfer without setting rc to exit (good/bad?)
-                            session.DGControl.PendingXfers.EndXfer(pending);
+                            session.DGControl.PendingXfers.Reset(pending);
                         }
                         else
                         {
@@ -122,7 +112,7 @@ namespace NTwain.Internals
                     }
                     #endregion
 
-                } while (rc == ReturnCode.Success && pending.Count != 0);
+                } while (rc == ReturnCode.Success && pending.Count != 0 && !session.CloseDSRequested);
             }
             else
             {
@@ -131,7 +121,8 @@ namespace NTwain.Internals
 
             // some poorly written scanner drivers return failure on EndXfer so also check for pending count now.
             // this may break with other sources but we'll see
-            if (pending.Count == 0 && session.State > 5)
+            if (//pending.Count == 0 && 
+                session.State > 5)
             {
                 session.ChangeState(5, true);
                 session.DisableSource();

src/NTwain/Properties/VersionInfo.cs

@@ -23,7 +23,7 @@ namespace NTwain
         /// <summary>
         /// The build release version number.
         /// </summary>
-        public const string Build = "3.3.9"; // change this for each nuget release
+        public const string Build = "3.3.9.2"; // change this for each nuget release
 
 
     }

src/NTwain/TwainSession.cs

@@ -393,11 +393,30 @@ namespace NTwain
             {
                 if (targetState < 7 && CurrentSource != null)
                 {
-                    ((ITwainSessionInternal)this).DGControl.PendingXfers.EndXfer(new TWPendingXfers());
+                    // not sure if really necessary but can't hurt to pin it
+                    var pending = new TWPendingXfers();
+                    var handle = GCHandle.Alloc(pending, GCHandleType.Pinned);
+                    try
+                    {
+                        ((ITwainSessionInternal)this).DGControl.PendingXfers.EndXfer(pending);
+                    }
+                    finally
+                    {
+                        handle.Free();
+                    }
                 }
                 if (targetState < 6 && CurrentSource != null)
                 {
-                    ((ITwainSessionInternal)this).DGControl.PendingXfers.Reset(new TWPendingXfers());
+                    var pending = new TWPendingXfers();
+                    var handle = GCHandle.Alloc(pending, GCHandleType.Pinned);
+                    try
+                    {
+                        ((ITwainSessionInternal)this).DGControl.PendingXfers.Reset(pending);
+                    }
+                    finally
+                    {
+                        handle.Free();
+                    }
                 }
                 if (targetState < 5 && CurrentSource != null)
                 {

src/NTwain/TwainSessionInternal.cs

@@ -28,6 +28,9 @@ namespace NTwain
         /// <value>The app id.</value>
         TWIdentity ITwainSessionInternal.AppId { get { return _appId; } }
 
+        bool _closeRequested;
+        bool ITwainSessionInternal.CloseDSRequested { get { return _closeRequested; } }
+
         void ITwainSessionInternal.UpdateCallback()
         {
             if (State < 4)
@@ -155,6 +158,7 @@ namespace NTwain
         /// <returns></returns>
         ReturnCode ITwainSessionInternal.EnableSource(SourceEnableMode mode, bool modal, IntPtr windowHandle)
         {
+            _closeRequested = false;
             var rc = ReturnCode.Failure;
 
             _msgLoopHook.Invoke(() =>
@@ -308,7 +312,9 @@ namespace NTwain
                     // some sources send this at other states so do a step down
                     if (State > 5)
                     {
-                        ForceStepDown(4);
+                        // rather than do a close here let the transfer logic handle the close down now
+                        //ForceStepDown(4);
+                        _closeRequested = true;
                     }
                     else if (State == 5)
                     {