Steps to reproduce the bug:
1. Create an editable document with some contents wrapped in an <h3> tag.
2. Put the caret inside the <h3> tag.
3. Try to run document.execCommand('inserthtml', false, $some_html) to insert some simple text into the current caret position.
4. Notice the inserted text looks different to the rest of the <h3> tag.
5. Print the HTML contents of the editable document to find some extra <span> tags have been inserted unintentionally by the InsertHtml command.
Created attachment 20471 [details]
Test case with an editable iframe prepared.
This bug is causing the bug https://dev.fckeditor.net/ticket/2113 in FCKeditor.
This is probably the same as bug 12248.
I've found that in addition to adding unnecessary <span> tags, the bug is also manipulating the DOM structure of the editable document in unexpected ways.
For example, if I had this HTML inside the editable frame:
<h3 style="color:red;">Hello <span id="abc" style="color:green;">Wor</span>ld!</h3>
.. and inside the green text "Wor", insert the "<" symbol, then we'll have:
<h3 style="color:red;">Hello <span id="abc" style="color:green;">W<span class="Apple-style-span" style="color: rgb(0, 0, 0); font-size: 16px; font-weight: normal; "><<span class="Apple-style-span" style="color: rgb(255, 0, 0); font-size: 19px; font-weight: bold; "><span id="abc" style="color:green;">or</span>ld!</span></span></span></h3>
Notice that now we have two <span> tags with the id "abc". This is clearly wrong.
*** This bug has been marked as a duplicate of 12248 ***