Index: trunk/src/org/openstreetmap/josm/actions/AbstractMergeAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/AbstractMergeAction.java	(revision 13131)
+++ trunk/src/org/openstreetmap/josm/actions/AbstractMergeAction.java	(revision 13132)
@@ -109,5 +109,5 @@
         JPanel pnl = new JPanel(new GridBagLayout());
         pnl.add(new JLabel(label), GBC.eol());
-        pnl.add(layerList, GBC.eol());
+        pnl.add(layerList, GBC.eol().fill(GBC.HORIZONTAL));
         if (GraphicsEnvironment.isHeadless()) {
             // return first layer in headless mode, for unit tests