Description of problem:
When one selects a mount point and clicks on "Customize..." to expand available options, list of mount points is resized and buttons bellow the list are moved down.

Version-Release number of selected component (if applicable):
anaconda 18.24

How reproducible:
always

Steps to Reproduce:
1. run installation in GUI mode
2. go to custom partitioning
3. create or select existing mount point and click on "Customize..."
  
Actual results:
List of partitions is resized, buttons (add, remove, ...) are moved.

Expected results:
List of partitions is not resized since there is no reason for it.