Undo function issues

Hi,

I had some issues using undo or ctrl+z in FCKeditor 2.6.3 and 2.6.4.

For example:

Write a word:
Support

After this, add a style like bold
Support

Now copy some text from notepad and paste replacing first word.
Help

Now use ctrl+z or undo button. The result expected is Support but you got Support without bold style.

Regards,
Pedro Muniz