Serious problem with vowelized Arabic in Gtk

[zalit gmx com]

I am sending again this email because the first time I sent it it did 
not go
through, because of a big file that was attached to it.

The screencast in the mediafire link below [1] shows a SERIOUS problem
with the rendering of vowelized Arabic text in gedit.
As you can see, as the cursor is moved along to select a text, the words
jump up and down.

This problem occurs not only in gedit, but also in the Bluefish editor,
also based on Gtk.
So I assume it is a bug in Gtk.

The key in reproducing the problem seems to be the use of the vowels in
the Arabic text, because texts without vowels have no such problems, as
far as I can remember.

The screencast shows gedit running under Windows 7. I don't know whether
this is a Windows-only problem or not.

I hope someone will take the time to look into this matter.

Cheers

Zafar

[1] http://www.mediafire.com/?roerf5ttfrxch80