Index: /FCKeditor/trunk/editor/_source/classes/fckenterkey.js
===================================================================
--- /FCKeditor/trunk/editor/_source/classes/fckenterkey.js	(revision 1082)
+++ /FCKeditor/trunk/editor/_source/classes/fckenterkey.js	(revision 1083)
@@ -418,4 +418,9 @@
 		if ( !oSplitInfo.WasStartOfBlock && !oSplitInfo.WasEndOfBlock )
 		{
+			// If the next block is an <li> with another list tree as the first child
+			// We'll need to append a placeholder or the list item wouldn't be editable. (Bug #1420)
+			if ( eNextBlock.nodeName.IEquals( 'li' ) && eNextBlock.firstChild
+					&& eNextBlock.firstChild.nodeName.IEquals( ['ul', 'ol'] ) )
+				eNextBlock.insertBefore( eNextBlock.ownerDocument.createTextNode( '\xa0' ), eNextBlock.firstChild ) ;
 			// Move the selection to the end block.
 			if ( eNextBlock )