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. Drag the block from first zone to the second zone. (screenshot 1)
6. Go to the dashboard by clicking on the 'eZ' logo in top left corner.
Issue: Application hangs with the dark overlay overing most of the window (screenshot 2). In browser console error occurs "Uncaught TypeError: Cannot read property 'style' of null" (screenshot 3).