Someone posted a picture a short while ago where a cleared ADV was present on the left DDI and the black line didn't mask the rest of the screen. Unfortunately, I can't find it right now, must be in one of the threads here that have been posted since the latest open beta patch.
Also, you can find an interview on Youtube with a pilot who states that they had the radar on the right DDI and the SA page on the left one most of the time. Now, there could be two reasons for this:
1. Maybe the pilots didn't care about the obscuring black lines or had no messages anyway which would lead to display symbology masking, whereas we do have messages/advisories all the time because a lot of systems aren't implemented yet.
2. Maybe it's due to different software versions, although I somehow doubt it.
ED has their SMEs though, so what do I know.