GNU/Linux Debian Squeeze 64 bits. This error appears too in a 64 bits windous build that I have tested too.
In 2.63a this bug is not reproductable.
when you try to modify last characters of long names such as This_is_a_datablock_with_a_loooooooooong_name , typing has a weird behavior, hiding final characters that seems to be actually here and thus ending with doubled characters on names and this kind of not crucial but annoying issues. This issue seems to appear whenever to name is longer than the available visible space in the textfield. To reproduce:
1- start with the default scene, select the cube, press N to open panel
2- Under "Item" subpanel, change the default name "Cube" to something longer, so it occupies more characters than the visible in the textfield
3- When changed the name, click again to the textfield to rename it. Go to the end and try writing/deleting/changing (in a "real life" simulation way) previous ending characters. You will see the problem.
Hope I'm explaining. Thanks for your work!