fixed http://community.sharpdevelop.net/forums/t/12236.aspx

src/AddIns/BackendBindings/VBNetBinding/Project/Src/CompletionDataHelper.cs

@@ -95,14 +95,21 @@ namespace ICSharpCode.VBNetBinding
 			
 			AddSpecialItems(ref result, info, resolvedType, m, expressionResult, editor);
 			
+			char prevChar;
+			
 			if (pressedKey == '\0') { // ctrl+space
-				char prevChar =  editor.Caret.Offset > 0 ? editor.Document.GetCharAt(editor.Caret.Offset - 1) : '\0';
+				prevChar = editor.Caret.Offset > 0 ? editor.Document.GetCharAt(editor.Caret.Offset - 1) : '\0';
 				word = char.IsLetterOrDigit(prevChar) || prevChar == '_' ? editor.GetWordBeforeCaret() : "";
 				
 				if (!string.IsNullOrWhiteSpace(word))
 					result.PreselectionLength = word.Length;
 			}
 			
+			prevChar =  editor.Caret.Offset > 0 ? editor.Document.GetCharAt(editor.Caret.Offset - 1) : '\0';
+			
+			if (prevChar == '_')
+				result.PreselectionLength++;
+			
 			result.SortItems();
 			
 			return result;

src/AddIns/BackendBindings/VBNetBinding/Project/Src/VBNetCompletionBinding.cs

@@ -125,6 +125,10 @@ namespace ICSharpCode.VBNetBinding
 								return CodeCompletionKeyPressResult.None;
 							if (IsTypeCharacter(ch, prevChar))
 								return CodeCompletionKeyPressResult.None;
+							if (prevChar == '_') {
+								result.Expression = '_' + result.Expression;
+								result.Region = new DomRegion(result.Region.BeginLine, result.Region.BeginColumn - 1, result.Region.EndLine, result.Region.EndColumn);
+							}
 							LoggingService.Debug("CC: Beginning to type a word, result=" + result + ", context=" + result.Context);
 							ShowCompletion(result, editor, ch);
 							return CodeCompletionKeyPressResult.CompletedIncludeKeyInCompletion;