diff --git a/TODO b/TODO
index f912237..9e49618 100644
--- a/TODO
+++ b/TODO
@@ -1,6 +1,5 @@
 Technology Preview 2 :
 - Fix the fog impression when cloud layer overlaps with ground range.
-- Fix forms with layers apply and revert buttons (when deleting last cloud layer, can't apply it).
 - Replace zone ranges with curves (with curve input and curve dialog).
 - Interface for textures thickness, slope_range and thickness_transparency (and correct slider ranges).
 - Render tab previews should not rerender when changing render options.
@@ -45,6 +44,7 @@ Technology Preview 3 :
 - Improve sky rendering (colors and light halo).
 - Add a progress indicator on previews.
 - Multi threaded first pass.
+- Mark modified tabs and ask for losing modifications (idem for layers).
 - Fix potential holes in land rendering.
 - Progressive final render.
 - Propose several backgrounds for water rendering (grid, sinus...).
diff --git a/gui_qt/baseform.cpp b/gui_qt/baseform.cpp
index 11a8fa9..27c9ac1 100644
--- a/gui_qt/baseform.cpp
+++ b/gui_qt/baseform.cpp
@@ -155,16 +155,27 @@ void BaseForm::applyConfig()
 void BaseForm::layerAddClicked()
 {
     layerAddedEvent();
+    
+    button_apply->setEnabled(true);
+    button_revert->setEnabled(true);
 }
 
 void BaseForm::layerDelClicked()
 {
     layerDeletedEvent(layer_list->currentIndex());
+    
+    button_apply->setEnabled(true);
+    button_revert->setEnabled(true);
 }
 
 void BaseForm::layerListChanged()
 {
+    bool changed = button_apply->isEnabled();
+    
     layerSelectedEvent(layer_list->currentIndex());
+    
+    button_apply->setEnabled(changed);
+    button_revert->setEnabled(changed);
 }
 
 void BaseForm::addPreview(BasePreview* preview, QString label)
diff --git a/gui_qt/basepreview.cpp b/gui_qt/basepreview.cpp
index 0f26635..d8cff7d 100644
--- a/gui_qt/basepreview.cpp
+++ b/gui_qt/basepreview.cpp
@@ -169,6 +169,7 @@ void PreviewDrawingManager::addChunk(PreviewChunk* chunk)
 
 void PreviewDrawingManager::removeChunks(BasePreview* preview)
 {
+    int removed = 0;
     for (int i = 0; i < _chunks.size(); i++)
     {
         PreviewChunk* chunk;
@@ -180,9 +181,12 @@ void PreviewDrawingManager::removeChunks(BasePreview* preview)
             _updateQueue.removeAll(chunk);
             _lock.unlock();
             
+            removed++;
             i--;
         }
     }
+    
+    logDebug(QString("[Previews] %1 chunks removed, %2 remaining").arg(removed).arg(_chunks.size()));
 }
 
 void PreviewDrawingManager::updateChunks(BasePreview* preview)
@@ -241,6 +245,11 @@ void PreviewDrawingManager::performOneThreadJob()
     }        
 }
 
+int PreviewDrawingManager::chunkCount()
+{
+    return _chunks.size();
+}
+
 /*************** BasePreview ***************/
 BasePreview::BasePreview(QWidget* parent) :
 QWidget(parent)
@@ -301,7 +310,7 @@ void BasePreview::stopDrawers()
 
 void BasePreview::reviveAll()
 {
-    logDebug("Reviving all previews");
+    logDebug("[Previews] Reviving all previews");
     _drawing_manager->updateAllChunks();
 }
 
@@ -400,6 +409,7 @@ void BasePreview::showEvent(QShowEvent* event)
 void BasePreview::resizeEvent(QResizeEvent* event)
 {
     QImage* image;
+    int added = 0;
 
     this->lock_drawing->lock();
 
@@ -418,8 +428,10 @@ void BasePreview::resizeEvent(QResizeEvent* event)
         for (int y = 0; y < _height; y += 32)
         {
             _drawing_manager->addChunk(new PreviewChunk(this, x, y, x + 32 > _width ? _width - x : 32, y + 32 > _height ? _height - y : 32));
+            added++;
         }
     }
+    logDebug(QString("[Previews] %1 chunks added, %2 total").arg(added).arg(_drawing_manager->chunkCount()));
 
     delete image;
 
diff --git a/gui_qt/basepreview.h b/gui_qt/basepreview.h
index 128da2f..356a6b8 100644
--- a/gui_qt/basepreview.h
+++ b/gui_qt/basepreview.h
@@ -117,6 +117,7 @@ public:
     void updateChunks(BasePreview* preview);
     void updateAllChunks();
     void performOneThreadJob();
+    int chunkCount();
 
 private:
     int _thread_count;
diff --git a/i18n/paysages_fr.ts b/i18n/paysages_fr.ts
index 1856135..3293356 100644
--- a/i18n/paysages_fr.ts
+++ b/i18n/paysages_fr.ts
@@ -29,7 +29,7 @@
         <translation>Annuler les modifications</translation>
     </message>
     <message>
-        <location filename="../gui_qt/baseform.cpp" line="279"/>
+        <location filename="../gui_qt/baseform.cpp" line="290"/>
         <source>Layer %1</source>
         <translation>Niveau %1</translation>
     </message>