common package is the common staff for both the A7 and A8 versions, containing system and graphics files, nearly everything, except the exe file and the exe specific dll-s.
so the only difference between A7 and A8 compilations is the exe and the system dll-s, this is why they can be downloaded separately.
I got crash only when I put MapBuilder into a very long named folder and wanted to make a screenshot by pressing space. And another crash situation was during entity placement, when I selected another entity to be placed by a hotkey, and placed it too fast: e.g. pressing 1, left click, pressing 2, left click within half a second. I always forget to resolve it.
And please be careful with wmb compilation, it calls the wwmp2wmb.exe, the editor gets minimized, so you can check compilation result, but the map compiler window must be closed afterwards, because the output files are copied only after this action to their proper folder. Probably later I modify it to be the compilation customizable.