try this: switch to node editor -> Compositing Nodes, then do a SHIFT+A to get the ADD Menu.
Now try to browse through the items in the submenu (eg. Input menu items) with the arrow keys.
Key "up" moves down and key "down" moves up in the submenus.
Tested on Blender 2.60.1 revision 41549 on windows 7 64 bit, compiled with
scons build system and VS 2008 x64.
It's because of how ui_handle_menu_event works -- it makes quite tricky checks in which direction movement happens depending on button type.
Not sure what's easier/safer: change logic of this function or change type of buttons used for nodes menu. Checked usages for uiItemV and found that it's used in node_editor only, so changes type of button used there. Attaching patch and assigning to Brecht to check if it's acceptable change.