Parent tag data-is is reset when disabling a nested tag with if="...

[vzdor]

<div data-is="message"></div>

When there is a nested tag in the message tag with an "if" attribute:

<message>
   <editor if="{editing}"></editor>

If I update the message tag with editing=false, then data-is, on the parent tag, is set to null.
It works if I wrap the editor tag in a div:

<div><editor if="{editing}"></editor></div>

2. Can you reproduce the issue?
   http://plnkr.co/edit/BzcSx89AzIX3wn0npZKl?p=preview
   Click the Close link and notice that the background (scoped class) is not applied.

3. On which browser/OS does the issue appear?
   Firefox 45, Chromium 57

4. Which version of Riot does it affect?
   3.2, 3.4

5. How would you tag this issue?

• Question
• Bug
• Discussion
• Feature request
• Tip
• Enhancement
• Performance