Inconsistent behavior when inserting <dt><dd> into a definition list with insertHtml

[wwalc]

1. Open _samples/api.html
2. Start with the following source and selection

   <p>first line</p>
   <dl>
   <dt>^definition1</dt>
   <dd>detail1</dd>
   </dl>
   

3. Paste into the textarea below CKEditor:

   <dt>definition</dt><dd>detail</dd>
   

4. Click "Insert HTML"
5. Results:
   IE - new definition list is created
   Firefox - dt/dd is pasted inside of exisitng definition list, but also an empty definition term is created:

   <dl>
   	<dt>
   		&nbsp;</dt>
   	<dt>
   		definition</dt>
   	<dd>
   		detail</dd>
   	<dt>
   		^definition1</dt>
   	<dd>
   		detail1</dd>
   </dl>
   

[wwalc]

Possibly related to #5309.

[j.swiderski]

Opera, IE have been creating two definition lists from CKE 3.5.3 Webkit has been creating three definition lists from CKE 3.5.3

Firefox has been inserting empty definition term from CKE 3.1