This is probably a privacy issue.

There have been times, such as this morning, where when I resume my laptop, I see content flash on the screen before the curtain is visible for a very short moment.

The content that is visible is no longer active. It seems to be from a Firefox session closed before the laptop was suspended.

This is a privacy issue because the contents could be quite sensitive, and a user should not need to think about the setting they are in when they open their laptop, only to discover they've potentially disclosed information about themselves.

It is quite possible that this is a driver bug as well. I can't make this happen every time, but the machine most recently that I've seen it on is a Macbook Air 13" from 2013. I do believe (but not positive) that I've seen it on my Dell 2710 desktop as well (which has hybrid graphics, but is using Intel GPU exclusively).

Feel free to move this to another project deeper in the stack if necessary (say mutter, or the likes).