Block border and preview get misaligned when slider visibility changes.

Prereq.: Landing Page exists (published) with e.g. Tag block and some content.

Steps:
1. Open the LP in edit mode.
2. Observe the border-preview alignment. [OK] (screen-shot 1)
3. Open the settings form.
4. Observe the border-preview alignment. [NOK] (screen-shot 2)
5. Change the browser window height (decrease it).
6. Close the settings form.
7. Observe the border-preview alignment. [NOK] (screen-shot 3)
8. Change the browser window height (increase it).
9. Observe the border-preview alignment. [OK] (screen-shot 4)

Actual: Refresh is triggered by window resize.
Expected: Refresh is triggered by slider visibility.