Let the handshake packet refresh the CUI protocol version (it happens that players join with another client before the previous session expires) and also send the current selection when receiving a handshake packet (for when the player joins and the previous session did not expire)

src/main/java/com/sk89q/worldedit/LocalSession.java

@@ -605,13 +605,12 @@ public class LocalSession {
     }
 
     public void handleCUIInitializationMessage(String text) {
-        if (hasCUISupport()) {
+    	if(!hasCUISupport()) {
-            return;
+    		setCUISupport(true);
     	}
     	
         String[] split = text.split("\\|");
         if (split.length > 1 && split[0].equalsIgnoreCase("v")) { // enough fields and right message
-            setCUISupport(true);
             try {
                 setCUIVersion(Integer.parseInt(split[1]));
             } catch (NumberFormatException e) {

src/main/java/com/sk89q/worldedit/bukkit/CUIChannelListener.java

@@ -41,5 +41,6 @@ public class CUIChannelListener implements PluginMessageListener {
         LocalSession session = plugin.getSession(player);
         String text = new String(message, UTF_8_CHARSET);
         session.handleCUIInitializationMessage(text);
+        session.describeCUI(plugin.wrapPlayer(player));
     }
 }