fix #236:

per http://www.blackwasp.co.uk/WPFItemsSource.aspx where it says:

> When ItemsSource is set, the Items property cannot be used to control the displayed values. If you later set ItemsSource to null, Items becomes usable again.

Flipped the ItemSource nulling and clearing of the list.

Qiqqa/AnnotationsReportBuilding/AnnotationReportOptionsWindow.xaml.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.ComponentModel;
 using System.Windows;
 using icons;
@@ -83,7 +84,7 @@ internal void ShowTagOptions(Library library_, List<PDFDocument> pdf_documents_,
             pdf_documents = pdf_documents_;
             OnShowTagOptionsComplete = OnShowTagOptionsComplete_;
 
-            // Collate all the availalbe tags
+            // Collate all the available tags
             HashSet<string> all_tags = new HashSet<string>();
             HashSet<string> all_creators = new HashSet<string>();
             foreach (var pdf_document in pdf_documents)
@@ -116,12 +117,14 @@ internal void ShowTagOptions(Library library_, List<PDFDocument> pdf_documents_,
 
             List<string> all_creators_sorted = new List<string>(all_creators);
             all_creators_sorted.Sort();
-            ObjFilterByCreatorCombo.ItemsSource = all_creators_sorted;
-
-            List<string> bindable_tags = new List<string>(all_tags);
-            bindable_tags.Add(HighlightToAnnotationGenerator.HIGHLIGHTS_TAG);
-            bindable_tags.Add(InkToAnnotationGenerator.INKS_TAG);
-            bindable_tags.Sort();
+            ObservableCollection<string> all_creators_source = new ObservableCollection<string>(all_creators_sorted);
+            ObjFilterByCreatorCombo.ItemsSource = all_creators_source;
+
+            all_tags.Add(HighlightToAnnotationGenerator.HIGHLIGHTS_TAG);
+            all_tags.Add(InkToAnnotationGenerator.INKS_TAG);
+            List<string> all_tags_sorted = new List<string>(all_tags);
+            all_tags_sorted.Sort();
+            ObservableCollection<string> bindable_tags = new ObservableCollection<string>(all_tags_sorted);
             ListTags.Items.Clear();
             ListTags.ItemsSource = bindable_tags;
 
@@ -190,9 +193,8 @@ protected override void OnClosed(EventArgs e)
             pdf_documents.Clear();
             pdf_documents = null;
 
-            ListTags.Items.Clear();
             ListTags.ItemsSource = null;
-
+            ListTags.Items.Clear();
         }
     }
 }