Like any wide open forums you find all kind of discussion and bugs reported by rookies up to experienced simulation professionals. And then it becomes very hard to deal with all noise into the threads.
Testing is a job by itself requiring, for a flight sim, knowledge in software architecture, real time processing, physics, AGILE (…) test strategy and test planning because it is extremely complex or complicated to test. The difference between Complex and Complicated can be found here in the Cynefin framework:
I wrote an article about what it takes to test a Full Flight Simulator and you can find in the article the suggested skills for a tester and what an extremely refined simulator can do in general.
For aircraft handling a base needs to be established: We call that a QTG. A QTG is a set of objective and subjective tests coming from EASA or FAA. This link is the list of tests that would catch many deviation in aerodynamics, atmosphere modeling, ground model, aircraft model. It is quite large doc but if you are curious about how we test real sims it is worth to have a peek at it:
The document covers also the visual, radios, special effects and malfunctions.
If you are a skilled tester and interested by test automation you might want to watch some one of the conferences I gave in different part of the world about testing complex systems.
I hope that the reading can shed some light about testing and if you want to dig deeper you can also read some articles from two of my conference colleagues: James Marcus Bach and Michael Bolton (From Toronto).