Getting stray characters

I'm getting unprintable characters appear after saving. In particular, they appear in table cells when the cell is blank (even if I add a space to the cell). They also appear in the body of the text in certain places.

I've attached an example of what I'm seeing. And I see the character in the source if I edit the post as well. Where is it coming from?

I'm using the latest version of CKEditor.

Is there any way of preventing such characters from getting created and saved?

Thanks,

doug

p.s. I can't get image URL to work here. They always show as broken images.