Modal bug when opening

I've had this bug/glitch before, but always managed to avoid it one way or another, but not this time.

In my application, when opening a modal dialog, I get some really strange behaviour. Parts of the dialog flicker or are even missing and the underlying view can partially been seen.
Screenshot here: https://postimg.org/image/avkpqoldl/

Currently using macOS Sierra (but also had this issue on previous versions), Chrome version 53.0.2785.143 (64-bit) and Vaadin 7.7.3.
I have no issues if I change any of this to either Safari or some Lunix distribution.

It can be recreated on the Vaadin Valo-theme demo page : http://demo.vaadin.com/valo-theme/#!common
When you open a dialog with 'closable', 'resizable' and 'modal' selected.

Open the dialog, start enlarging it and it will happen at a certain point.

UPDATE:
If I fill the dialog with components that are full sized, I don't get the issue anymore. So far. I'll keep on testing.

Aaaaaaaand the issue is back.

For no reason what so ever.