I have MC CAS settings set to allow clothing to be available for all ages and hair and accessories to be set for both gender and all ages. But when I dress an elder sim in adult clothing and makeup, etc. the game automatically reverts everything to different clothing. At first I didn't think it was MC causing the issue.
But then I remembered that after putting a female hair on a male sim that it would revert to bald or some random male hair once I went back to gameplay. So, I assumed that this function of MC just didn't function properly. Is that correct? Does this normally work properly or could it be another mod causing the issue?
I did try removing all mods including MC and couldn't duplicate the issue.

Sorry, I'm a little confused. If you remove MC, then you will be using EA's version of CAS and its subsets (Change Appearance, Plan Outfit, etc.) so the MC CAS settings wouldn't apply anymore.

This has been reported before but I don't think any of us were able to re-create the issue. A question though, when you do have MC and its option set that way, do you also have the MC Integration module in play?

Yes I tried to recreate it before and was unsuccessful so there's a condition I'm not finding or they are somehow ending up in EA CAS.

I just meant that I couldn't duplicate the issue after removing MC (and all mods) so therefore I assumed it was MC that was causing my issue. I didn't originally think it was a mod causing the problem. But after I removed all my mods I realized that all the clothing that I had put on the elder sim whose clothes were changing were no longer in the catalog. I remembered that I had that all age option set up with MC so I was dressing my sim in adult clothes when I hadn't realized. So, that's obviously why the clothes no longer showed up in the catalog after I removed all mods. That made me realize that her clothes were probably reverting back (earlier before removing MC and mods) because I was dressing her in "adult" clothing. Sorry, I realize that still sounds a little confusing. I'm not sure how to be clearer.
Basically that function in CAS doesn't work for me.
And yes, I do have the Integration Module installed as well.

I'm having this exact same issue. I enabled the "Accessories enabled for all genders" under CAS in Master Controller, as I like using male and female accessories interchangably. I made a female Sim the other night that I had wearing a pair of male glasses and a male tattoo accessory (either a ring or glove slot) and saved her to the Bin. Tonight I loaded up that Sim, and noticed that her tattoo was simply missing, and the game had replaced her glasses with a random female accessory from the glasses slot.

When I entered CAS with her, and put the items back on her (they appear just fine in CAS, mind, and show up just fine on the Sim in CAS), I notice that as soon as I switch off of that outfit, if I switch back to that tab, the game has already removed them. I can't keep the male accessories on her, and I can't figure out why.

I have all the latest versions of Master Controller, Master Controller Cheats, Master Controller Integration, the expanded tattoo, and the tattoo locations. I do have a lot of mods installed, but the only ones (sliders aside) that have anything to do with CAS is cmar_SkinTonePanel1.38 and Shimrod_CaSCamZoomInPets138 . I tried removing both of those and the problem persisted. This is really driving me crazy; I'd really love to dress my female and male Sims with accessories for the other gender. -_-;;

It remains puzzling that we still cannot re-create this issue.

Leaving out saves to the bin for a moment, do you get any different results if you take your sim into CAS, dress and accessorize them the way you want on one outfit, save and leave CAS without switching categories? Or does the same thing happen?

Well, if I don't switch any outfit tabs in CAS, then yes, it will save the changes. So at the moment the only way I'm able to get that pair of glasses and tattoo on every outfit is by using Basic > Change Outfit, going into CAS, changing it, saving, and doing that each time just to change it, which isn't exactly optimal. -_-;; Something about swapping the outfit tabs in CAS immediately removes the mismatched gendered items from the previous outfit.

Actually, I only seem to be able to get the changes to apply to a single outfit at a time, even using the method above. Whether a swap a tab or not, the mis-gendered items disappear from the outfits I changed previously.

That wasn't really meant to be an optimal suggestion for gameplay, was just collecting more information about when and where the unwanted swaps happen. We'll have to await further comment from our developer.

Another suggestion though, you might consider (if on Patch 1.67 or below) using EasyCASP Editor to change the nature of these accessories so that they are available for both genders. Or use S3PE to accomplish the same if they are package based CC items. That's kind of extreme if you have hundreds of such items to work with and EasyCASP does not work on Patch 1.69, but just a thought.

I am on Patch 1.67 as I use the Steam version of Sims 3. I've just always felt myself miserable at having to manually edit/modify cc items myself. That's why I was looking into this particular option in Master Controller in the first place. I write Simlit and had a story idea in the works that uses a lot of animal cc that, unfortunately, is often either female-only or male-only, and I want to be able to equip it to either gender. If this doesn't work, I guess I'm going to have to learn how to edit the files but it has always seemed very daunting.