core Dynamic Page with multi columns cannot hide the dropdown menu when column is closed

[Meggie886]

Is it a bug ?
Yes
Which version ?
All of the versions, I used the latest

There are two questions :

1. why is the buttons is hidden in the third column at the start? Seems there is enough space

2. This is the explain for question 1. When I expand it ,shows all of the buttons, and then click collapse,the buttons still show on the page without overflow buttons.

3. The popup menu still shows when I close the last column.

Code Expample Link
https://stackblitz.com/edit/vyo1t3hr?file=src%2Fapp%2Fflexible-column-layout-example.component.html,src%2Fapp%2Fflexible-column-layout-example.component.ts

step1. open the column3 , then click the overflow button, a popup menu shows
step2. click the create button to close the column3, the popip menu still on the page