Repeater expands bug

Why original box of repeater expands sometimes when I added another box in repeater with the same height of original one?

There’s an original container box when we add repeater, right?
If I add any other things except for container boxes additionally, it’s fine.
If I add container boxes, repeater got expanded automatically when I refresh the Wix Editor page and open the page again or when I zoom out a little bit.

1st one happens every time. 2nd one, zooming out, doesn’t happen sometimes.
Is it known bug or my bad design?
Can anyone suggest me?
Thank you for your time.