dialog.position.js error when adding media

I have a custom form open in a modal that i think has been working Well. Recently noticed the overlay appears but modal is hidden. Any slight manual reside of the browser window makes it appear.

It seems to be more of an issue with FF than with Chrome; but have intermittently seen the issue with Chrome.

It seems to reliably work for Anon users (but not for admins).

Disabling Back To Top and it seems to reliably work. Which is odd as BTT is there for Anon.

Seeing same behavior,: disabling BackTotop makes it work.

The above solution works for me.

The window object is replaced with the document and deprecated jQuery .scroll() with the .on("scroll").

See:
https://api.jquery.com/scroll/
https://api.jquery.com/scroll-shorthand/

acke → closed merge request !16

drupgirl → changed the visibility of the branch 3190370-dialog.position.js-error-when to active.