Can not use arrow keys inside editing area with a frame

Hi,

I got a problem when using arrow keys to move the cursor inside the text editing area of FCKEditor:

This only happens when my page contains frame or iframe, for instance, the page contains two frames, the FCKEditor is inside one of those; or a page with FCKEditor contains an iframe.

When without any frame, the arrow keys works fine.

FCKEditor version: 2.6.5
Browsers: Firefox 3.6.x

Any idea why, is it a bug or not?

thanks in advance.