Unknown block leaks the blockquote

[0nko]

1. Start with a blank editor
2. Add an <unknown></unknown> in HTML mode
3. Switch to visual and tap on the question mark to open an unknown element dialog
4. Change the HTML to <unknown><blockquote>a</blockquote></unknown>
5. Tap on the Save button
6. Notice that "a" incorrectly appears below the unknown block (without the quote style)
7. Switch to HTML
8. Notice it is <unknown></unknown><blockquote>a</blockquote>
9. Switch back to visual mode
10. The quote style is now visible