Keyboard layout automatically replaced by default US

[foregam]

Release: Ubuntu 10.04.3 LTS
Kernel: 2.6.32-33-generic / amd64
gnome-applets 2.30.0-0ubuntu2

I work with multiple languages on a daily basis and all four keyboard layout slots provided by GNOME are occupied. A few days ago I created a new US layout which is slightly optimized for my programming needs and now use it by default. However, if I logout and login again, the fourth layout is replaced by the default US one. So I have:
1. US Programmer (Latin script)
2. Greek script
3. Hebrew script
4. Extended Arabic script ← replaced by basic US

How can I fix this?
Side note: Is the four layouts limit a bug or a perceived feature?

TYIA

The new layout:

partial alphanumeric_keys
xkb_symbols "alt-prog" {
  name[Group1]= "USA - Programmer";
  include "us"
  key <AE09> { [ 9, braceleft ] };
  key <AE10> { [ 0, braceright ] };
  key <AD11> { [ parenleft, bracketleft ] };
  key <AD12> { [ parenright, bracketright ] };
  include "level3(ralt_switch)"
};