Resize Handles inconsistent between FF and IE

Does anyone know how FCK determines what can have resize handles? Our clients use FCK to create HTML email messages that they send to their opt-in memberships. We typically create a base message based on their web site, for branding and so the email recipients know the emails are coming from a source they have a relationship with. Our UI lets them copy the base message to new mail issues, and tweak the content (using FCK). Base messages are as simple or as complex as the client's web site design.

We have one client whose base message is very CSS driven, with nested divs, aligned/floated divs, and no tables. On IE I can click in a variety of places and get resize handles around chunks of the document. On FF I can only get handles on the client's logo image in the top left. Even on IE, it doesn't seem like I can get handles on all the divs, and when I try a simple test document with nested divs I can't get handles at all. I've also noticed on both browsers that when resize bars are active on an element that's larger than the edit area, the grabbers display outside the edit area. I've tried this HTML in the nightly build with the same results.

Are there rules for what can have resize bars? Is it a bug that I'm not getting them on FF? (Is it a bug that I AM getting them of IE???) Is this simply browser-dependent and IE has some capability FF doesn't - I know there's browser-dependent selection logic in FCK.

I realize this post is a little vague. I didn't post code because there'd be rather a lot of it, since I've been unsuccessful at paring down to a test case. Any insights greatly appreciated.