Cannot read property error when scrolling in view mode with open console.

Steps:
1. Create new LP.
2. Add Tag block with one paragraph.
3. Publish.
4. Edit this LP.
5. Add another paragraph to the Tag block.
6. Publish.
7. Open browser console and have it in 'dock at bottom' mode.
8. Scroll the preview.
Issue: "Uncaught TypeError: Cannot read property '1' of null" exception is printed many times (attached).

Remarks: Also notice the extra area beneath the footer when scrolling (2nd screen-shot).