Hidden fields defined inside the editor, inserted with the appropriate toolbar button, are not being displayed. They are being correctly inserted in the code instead.
A icon should be shown instead, just like in Firefox.
ATM I can't figure out how the hidden field is inserted, there's no execCommand performed, and no queryCommandSupported/Enabled called. The hidden field must be in the DOM, because it shows up when you use the Source ... toolbar button, but I can't know for sure because I can't inspect the DOM of the editable subframe (the editable subframe has a custom contextual menu that doesn't include Inspect Element).
The hidden field "magic" is simply done with CSS:
border:1px dotted #FF0000 ;
content: "" ;
I've tried the above definitions with <span> and it worked well. So, I believe that the CSS selectors are working properly.
Probably the buggy thing here is "display:inline". Maybe WebKit is just saying "hidden is hidden", and doesn't do any work to possibly display those kings of elements. I really don't know, it is just a guess. If this is true, we could open a dedicated ticket for it.
I think I'll be able to make changes in the editor to not use CSS for it. I'll work on it now. I'll come with more news soon.
Ok, I was able to fix it in the editor code. It doesn't anymore uses styles to display hidden fields, which are now replaced with an image during editing.