{solved} Necklace diffuse texture appears on head

Hello all. I am attempting to create a custom necklace (for lack of a better term)-- a set of headphones that sits around the Sim's neck. It should look like below:

s4s preview headphones on neck

As you can see in the above image, the model looks fine in S4S's preview. It also looks fine in Blender. However, when I attempt to use it in the game proper, it starts running into problems. More specifically, the diffuse texture appears on the sim's hair with some outfits! If it does not appear on the sim's hair, then the hair's diffuse texture will replace the object's diffuse texture, which looks about as good as you'd think. With some shirts, there is the additional effect of see-through faces, usually shaped like rectangles on the chest area. Here are some examples of the effect in action:

texture on hair and missing faces -- young male
close-up view of texture on hair and missing faces -- young female, front
view of issue from back -- young female, back
hair texture on headphones

Some fixes that I have tried that haven't helped/created their own problems:

• Shadow map adjustments. The problem quite possibly comes in part from the shadow map, as the display did change when I changed it-- however, this caused black lines to appear on the Sim's arms and neck, which I think only happens when the shadow maps attempt to read a completely transparent area. I tried changing the map from one that had no transparencies to one that was all transparent save a rectangular area containing white and the shadow I wanted to add, as well as one that was all transparent with white only backing the areas containing the shadows, but to no avail. Either black lines appeared or the diffuse textures were messed up somehow. If I remove the shadow map, the diffuse map still gets screwed up.
• UV map. I checked that the UV maps were aligned properly on the diffuse texture and they were. I tried removing uv_1 and nothing changed. I tried removing the double vertices (to my knowledge, anyway) and nothing changed.
• Region map. I made sure that the region map contained all the effected areas (meaning the necklace, necklace shadows, and chest), was connected to the right geometries, and was placed in a high-numbered layer.
• Move the diffuse map. I tried to put the diffuse map elsewhere in relevance to the Sim's body, namely under the hands on the base diffuse map. This caused the map to change where it was incorrectly appearing-- for example, if the headphones map was placed under the hands (with the corresponding uv map adjustments), it would appear on the Sim's leg in CAS rather than the hair.
• Update the Sims 4, S4S, and Blender. Self-explanatory, didn't change anything about the issues.