undo spans does not work in IE

Hi everyone,

We've been makin an interesting project with CKeditor and we're using an additional layer to show triangles to visually show where a style is located so it is easier for the customer to see and correctly change these spans (otherwise you're left with a lot of span tags after some time).
The problem now is that the undo function is not working for spans in Firefox. The undo isworking for bold italic and so on but we need to get it working on spans as well....

Doens anyone have an idea how this can be resolved?

Thanks in advance for your time and effort