Dropzone covers block menu.

Steps:
1. Create new Landing Page with layout 1_2.
2. Add one block to left zone.
3. Add another block to left zone.
4. Add one block to right zone.
5. Remove the block from the right zone.
6. Try to remove the second (bottom) block from left zone.
Actual result: Right dropzone covers the block's menu.
Expected result: It's possible to remove block, menu is not covered.

Remarks: Please see attached, 'has-selected-block' is not removed, z-index stays '999'.