Channel Manager: White overlay and no spinner while page is loading

When opening a channel in the Channel Manager, there used to be a "spinner"/loading icon overlayed on the website part until the page has finished loading.

In 7.7 this was present.
In 7.8 the spinner only shows before any part of the page is loaded and there is nothing over the page to indicate that the page is still loading.
In 7.9 (trunk) the spinner only shows before any part of the page is loaded and there is a semi-transparent white(-ish) overlay until the page is loaded. Moreover, the spinner in the top left doesn't react at all to the Channel Manager being busy.

See attached screenshots for each version while the page is not fully loaded yet.