After bug 353304 was closed, someone commented that "Shift+Tab" no longer worked as he expected. (Starting at http://bugzilla.gnome.org/show_bug.cgi?id=353304#c17). The problem is that clients are inconsistent about whether Shift+Tab is "Shift+Tab" or "ISO_Left_Tab".

I've just discovered that the RFB protocol spec actually discusses this case and recommends that servers *should* have a special case here:

• There is no universal standard for “backward tab” in the X Window System.
  On some systems shift+tab gives the keysym “ISO Left Tab”, on others it gives
  a private “BackTab” keysym and on others it gives “Tab” and applications tell
  from the shift state that it means backward-tab rather than forward-tab. In the
  RFB protocol the latter approach is preferred. Viewers should generate a shifted
  Tab rather than ISO Left Tab. However, to be backwards-compatible with ex-
  isting viewers, servers should also recognise ISO Left Tab as meaning a shifted
  Tab.