Jittering in ComboBox component

Hi, I have a problem with the combo box component in Vaadin 14.
When i place the combo box on the bottom of a container there is a short jittering when i open the drop down list.
It seems there happens some kind of resizing in the background (scrollbar on the right is visible for some milliseconds).
This phenomen happens only when the combo box is on the bottom of a container and the drop down is opened for the first time.

I have uploaded a small demo project which shows the problem (https://github.com/xxSlashxx/combobox.git) and a animated gif in the attachment.
Any ideas how to fix that problem?