diff --git a/ide/filereferencelist.pas b/ide/filereferencelist.pas
index e3a08c9057..de08c02728 100644
--- a/ide/filereferencelist.pas
+++ b/ide/filereferencelist.pas
@@ -86,6 +86,7 @@ type
     function CreateFileList: TStringList;
     property TimeStamp: integer read FTimeStamp;
     property OnChanged: TNotifyEvent read FOnChanged write FOnChanged;
+    property UpdateLock: integer read FUpdateLock;
   end;
   
 implementation
@@ -175,7 +176,6 @@ end;
 procedure TFileReferenceList.Invalidate;
 begin
   IncreaseTimeStamp;
-  if not (frfSearchPathValid in FFlags) then exit;
   Exclude(FFlags,frfSearchPathValid);
   if FUpdateLock>0 then
     Include(FFlags,frfChanged)
@@ -211,7 +211,7 @@ end;
 
 procedure TFileReferenceList.EndUpdate;
 begin
-  if FUpdateLock=0 then RaiseException('TFileReferenceList.EndUpdate');
+  if FUpdateLock<=0 then RaiseException('TFileReferenceList.EndUpdate');
   dec(FUpdateLock);
   if (frfChanged in FFlags) then begin
     Exclude(FFlags,frfChanged);
diff --git a/ide/main.pp b/ide/main.pp
index 4ba17daa53..70186361e0 100644
--- a/ide/main.pp
+++ b/ide/main.pp
@@ -4918,13 +4918,16 @@ function TMainIDE.CreateProjectObject(ProjectDesc,
 begin
   Result:=TProject.Create(ProjectDesc);
   // custom initialization
+  Result.BeginUpdate(true);
   if ProjectDesc.InitProject(Result)<>mrOk then begin
+    Result.EndUpdate;
     Result.Free;
     Result:=nil;
     if FallbackProjectDesc=nil then exit;
     Result:=TProject.Create(FallbackProjectDesc);
     FallbackProjectDesc.InitProject(Result);
   end;
+  Result.EndUpdate;
 
   Result.MainProject:=true;
   Result.OnFileBackup:=@DoBackupFile;
diff --git a/ide/project.pp b/ide/project.pp
index dcc18f74ef..a15e00a3b5 100644
--- a/ide/project.pp
+++ b/ide/project.pp
@@ -1204,15 +1204,15 @@ begin
   if FSourceDirNeedReference then begin
     if not SourceDirectoryReferenced then begin
       fLastDirectoryReferenced:=GetDirectory;
-      Project.SourceDirectories.AddFilename(fLastDirectoryReferenced);
-      //DebugLn('TUnitInfo.UpdateSourceDirectoryReference ADD File="',Filename,' Path="',Project.SourceDirectories.CreateSearchPathFromAllFiles,'"');
+      //DebugLn('TUnitInfo.UpdateSourceDirectoryReference ADD File="',Filename,'" Project.SourceDirectories.TimeStamp=',dbgs(Project.SourceDirectories.TimeStamp));
       FSourceDirectoryReferenced:=true;
+      Project.SourceDirectories.AddFilename(fLastDirectoryReferenced);
     end;
   end else begin
     if SourceDirectoryReferenced then begin
-      Project.SourceDirectories.RemoveFilename(fLastDirectoryReferenced);
-      //DebugLn('TUnitInfo.UpdateSourceDirectoryReference REMOVE File="',Filename,' Path="',Project.SourceDirectories.CreateSearchPathFromAllFiles,'"');
+      //DebugLn('TUnitInfo.UpdateSourceDirectoryReference REMOVE File="',Filename,'" Project.SourceDirectories.TimeStamp=',dbgs(Project.SourceDirectories.TimeStamp));
       FSourceDirectoryReferenced:=false;
+      Project.SourceDirectories.RemoveFilename(fLastDirectoryReferenced);
     end;
   end;
 end;
@@ -1976,7 +1976,7 @@ begin
       SessionStorage:=StrToProjectSessionStorage(
                         XMLConfig.GetValue(Path+'General/SessionStorage/Value',
                                  ProjectSessionStorageNames[pssInProjectInfo]));
-      DebugLn('TProject.ReadProject SessionStorage=',dbgs(ord(SessionStorage)),' ProjectSessionFile=',ProjectSessionFile);
+      //DebugLn('TProject.ReadProject SessionStorage=',dbgs(ord(SessionStorage)),' ProjectSessionFile=',ProjectSessionFile);
 
       NewMainUnitID := xmlconfig.GetValue(Path+'General/MainUnit/Value', -1);
       AutoCreateForms := xmlconfig.GetValue(