For me, if I open a second copy of the same database, the first-opened copy gets moved to the right pane and the second-opened database appears as the left pane. I can make/SAVE any changes I want in the first-opened copy (on the right) without issue. BUT, if I make any changes through the second-opened copy (on the left), the changes get saved BUT upon closing that second-opened copy... Rootsmagic.exe access violations start popping up as soon as you resize the first-opened copy by dragging its left vertical border to the left. And the access violations continue until you close out the first-opened database and re-open it. That's my observation.
I'm getting more and more access violations and other such RM errors as time goes by. I do not know what is causing them. I do keep my RMGC file in my Dropbox folder, but I always pause Dropbox when I'm using RM. And in general I do use SQLite to produce reports, but I don't do it very often and the access violations happen regularly even if I haven't used SQLite in weeks. I do not know what is causing the increase in access violation errors. I did get a new computer last fall which is much faster than my old one, and I'm now on Windows 10 instead of Windows 7. But the various access violation errors were happening on my old machine and on Windows 7.
I have a theory of what's going on but I have no way to prove it. I can observe that RM has lots of threads running, and threaded operations are inherently asynchronous and therefore are inherently in need of synchronization from time to time. I don't know what all the RM threads are doing, but WebHints are surely running asynchronously in threads. Whatever these threads are doing, if they don't synchronize with each other properly then all kinds of bad things can happen such as access violation errors and corrupted databases. So I guess it seems to me that RM might possibly have some very subtle errors in its internal thread management. Such errors (if indeed that's what the problem is) can be devilishly difficult to diagnose and fix because they can be totally unrepeatable.
The errors you are seeing with two RM databases open at the same time are news to me in the sense that I have never encountered them. They could be thread related or they could be something else. If the symptoms are as repeatable as you suggest, then I would urge you to open a ticket and let the developers take a look at the problem. They might or might not be able to replicate the problem, but it would be good for them to take a look. And even if they can replicate the problem they might or might not be able to fix it easily in RM7. But surely it would be good to avoid having RM8 delivered with such problems.