WordPress adding <div> tags in place of <p> tags!

Has anyone experienced this before? Every time one of my clients makes a change to one of her WordPress Pages, it goes crazy and adds a <div></div> in place of all the <p></p> tags. What is happening??? On other sites I’ve seen the page code change just from switching from HTML to design view but this is crazy. Well, they’re both crazy.

Thanks much in advance!