XSS on personal message when you enter more than 1000 characters

1. Open Messages->New message
2. Enter following text to the message field:
<input style="background-position: center center;" class="inputtext" type="text" id="edit_activity_text" name="edit_activity_text" value="« maxlength=»160" onblur="return activity_editor.blur ();" onkeypress="return activity_editor.handle_key_press (event);" />после чего заменить его на следующий: <textarea id="edit_activity_text" name="edit_activity_text" onblur="return activity_editor.blur ();" ></textarea><input style="background-position: center center;" class="inputtext" type="text" id="edit_activity_text" name="edit_activity_text" value="« maxlength=»160" onblur="return activity_editor.blur ();" onkeypress="return activity_editor.handle_key_press (event);" /><input style="background-position: center center;" class="inputtext" type="text" id="edit_activity_text" name="edit_activity_text" value="« maxlength=»160" onblur="return activity_editor.blur ();" onkeypress="return activity_editor.handle_key_press (event);" />после чего заменить его на следующий: там там там там там там тамй<script>alert('Hi')</script>
3. Click Save or Send button

actual result: Dialog Box appears with button "OK" and message "Hi"
expected: error message appeasr with test "should be 2-1000 characters"