Thank you for listing the issues. I'll try to cover each one of them.
About 1): It seems to me, that this method has try-filter construct inside the code (you can check this by switching JustDecompile to IL, and see if the "filter" keyword appears anywhere in the code). If this is the case, then that's known issue, as JustDecompile doesn't really support try-filter and try-fault constructs.
About 2): The lines you've added are marked with the [CompilerGenerated] attribute. This means, that JD doesn't have to output that member (in this case a field, but it can be a method or even whole class) as it will be generated by the compiler. We intentionally do not write such members during project generation, as they might make your projects unbuildable (for instance the name of the compiler-generated field will collide with the name of the field the compiler wants to create and this will cause an error).
I guess the issue for MySettingsProperty is that it's marked as [CompilerGenerated] as well. Would you please check if this is the case.
If you stumble upon any other strange things in JustDecompile, please do tell us. As Vladi said, it's better to have a bug reported multiple times, than miss it.