Sims 3 CAS acting weird

@Evergreenium  There are a few different reasons this might happen.  The easiest first step is to quit and delete the five cache files in your Sims 3 game folder in Documents; they should be deleted regularly anyway, and definitely any time you add or remove content from your game.  For reference, the files are:

• CASPartCache.package
• compositorCache.package
• scriptCache.package
• simCompositorCache.package
• socialCache.package

Another possibility is that the sims were created using custom sliders that you don't have installed.  In that case, they'd initially appear one way but revert to using base game sliders when modified in CAS.  (This might not happen right away, so it could explain why one sim changes when you switch to another sim and back again.)  The download pages for the sims should list whether they use custom sliders or other mods or cc, but not all creators do so.

If neither of these helps, you can try adding the downloaded sims to a clean game folder and experimenting with them there.  How to get them into a clean folder will depend on whether they come with cc, and how you installed them in the first place.  So let me know, and I'll write out instructions.

Also, if you'd like me to check them out in my own game, you can PM me the links to a couple of the sims.  (Please don't post them in this thread; direct links to third-party content are generally not allowed.)  I'll see if I can figure out what's going on and let you know.