Go to the Tools menu and choose Filtering. Select a filter and press Alt+D and nothing happens, because Alt+D means both "Delete" and "Down". The same problem exists in the windows shown when clicking both of the "Define..." buttons. The shortcut key should be changed for one of the buttons so that both actions can be triggered using keyboard shortcuts.
Changes related to this bug have been committed. Please check latest Git and update the bug accordingly. You can also get the patch from: http://git.claws-mail.org/ http://git.claws-mail.org/?p=claws.git;a=commitdiff;h=0d8e6129533572a8a637d61bb968a0b6160f0283 Author: Paul <paul@claws-mail.org> Date: Wed Aug 14 08:51:16 2013 +0100 fix bug 2986, 'Down and Delete buttons have same hotkey in filtering config' and then some