Legit the most infuriating thing, I can't stand it. If you don't realize it, lemme give you some proof.
Here is a base Ash prime with the Bai Hu skin on and prime details turned on. Notice the smoke coming from his left arm (the arm on the right side of the image if you gotta think about it for a sec), now if I were to turn it off, it looks like this:
You know what's even more confusing and annoying? Turning on prime details and using the deluxe skin causes this to happen as well, meaning for his deluxe, it's at least seemingly intentional, have a look:
And to top it all off, if you turn prime details off, then switch to Ash, Ash prime, or Ash Immortal, it causes the smoke arm to come back, as well as the armor for the non-base Ash skins, so it's gotta be something intentional towards the Warframe and not the skins right? Also Ash's immortal skin doesn't let you toggle his prime details either, this admittedly isn't that *huge* of a problem since a lot of other immortal skins don't allow for prime details to be toggled, but it's something to note.
Again though, I have to ask, why is this a thing? I mean it's probably something crazy and super small to complain about but I'd imagine it's an extremely easy fix right?