Application hangs when switching from Edit mode to the dashboard.

Steps:
1. Create a new Landing Page with layout 2_1.
2. Add a Schedule block to the first zone.
3. Choose template list.
4. Add a content item.
5. Move the block to the second zone. (screenshot 1)
6. Go to the dashboard.
Issue: Application hangs with the dark overlay overing most of the window (screenshot 2). In browser console error occurs "Cannot read property 'className' of null" (screenshot 3).

Remarks: Causes tests on Jenkins to fail.