Opening portal causes content to jerk

I’ve recently noticed that when opening Portal the contents of the screen jerks to the right. Reason being, Portal is now causing the vertical scroll bar to disappear. I don’t know when exactly this starting happening, but it wasn’t occurring in version 4.41.x and did start to occur when I updated to 4.47.x. I’m on Ghost(Pro) now though, and it still occurs there with 4.47.4.

It’s sometimes hard to see the issue occurring on sites that use several tiers (such as The Browser) since the overlay largely covers up the underlay, but is readily obvious on sites that simply use the subscriber functionality.

I’ve looked at dozen of sites and it occurs on every single one of them but one, a site that rhymes with Binge and Purge. If you want to see the bug in action check out, for example, Headline, and just click on the Portal or Subscribe buttons.

I was fortunately able to fix this on my own site via forcing the vertical scroll bar to be permanent, although I’m not sure if this is good practice or not.

body {
  overflow-y: scroll !important;
}

Edit: that should have been overflow-y, not overflow.

I’m not able to reproduce this in latest Chrome, Safari or Firefox