As I work on a quite big commissioned work I have to do lots of things in CC3.
We work with over 60 different characters, all of them made by my client but sometimes things has to be reconsidered.
Or hair/mustache/beard was set up as cloth and I have to make them "real hair" for facial expressions.
One thing I noticed and really is annoying, as soon I turn things into accessory instead of cloth,
hidden meshes on body are removed, though on clothes they remain...
WHY???
It's a PITA to always redo the same things without a reason...:pinch:


Toystorylab on Vimeo :     Crassitudes (my "Alter Ego") on Youtube: 

BUMP!
Sucks RL does not feel the need to reply...

Toystorylab on Vimeo :     Crassitudes (my "Alter Ego") on Youtube: 

You've asked your question.  No one responded right away.  But then, you want slam "RL" with this statement, "Sucks RL does not feel the need to reply..."  Personally, I see that as an untrue statement.
Have you stopped to consider that perhaps the right person has not yet had to time to review your post, let alone respond? I don't think that people just sit around waiting to jump on and respond to posts.
People have jobs and other responsibilities - even working on their own projects.  Personally, I have responded to a number of posts - howbeit, when I have experienced the same or a similar problem.
Other than that, if I don't have the answer to the problem itself, I simply leave it alone, and wait for someone with more experience, i,e, someone who is familiar with the problem, to take a stab at it. 
I have even made some posts over the years, some were answered within the hour, Others took a little longer.  The key here is to be patient. I'm sure that your question(s) will eventually get answered.
But when you make false statements like you did, after you haven't gotten a response, personally, I think that it turns people off, and make them reluctant to get involved. 
My suggestion: Learn to be patient!  If your question is not answered right away, it's not the end of the world.

I am unable to answer the question, as I have not encountered it. Thus, I have no idea what is going on.
 

I think you meant the hidden mesh becomes unhidden, rather than being removed?

The hidden mesh is a feature of the clothing. If you need to transfer the skin weights again, there is no need for the intermediate step of converting to an accessory. You can just transfer the weights again on an already rigged clothing item.

Well, I was patient for 3 weeks... :D


Toystorylab on Vimeo :     Crassitudes (my "Alter Ego") on Youtube: 

Yeah, sorry, hidden mesh of my body becomes unhidden...
Example of what I do:
So I have my body mainly hidden to prevent poke through.
Did that with selected character and edit mesh (not the hide body option for clothes)
Also hid meshes partially for shirt under coat and the same with vest above shirt under coat.
Now I have a moustache that is cloth.
To change it from cloth to facial hair I first have to make it an accessory,
before I can use "create hair, brows, beard" at all.
Though as soon I do so, the hidden mesh of my body becomes unhidden.
And that sucks.
Is this a bug or normal behavior?
And if so, WHY???
Here I made a quick video to show what I mean:

So why are my hidden meshes of my body unhidden after using convert to accessory for something totally different,
though the hidden meshes of the cloth remain.
Makes no sense to me...

Toystorylab on Vimeo :     Crassitudes (my "Alter Ego") on Youtube: 

I completely agree with Toystory here. It is not normal.
You spend quite some time carefully custom hiding body mesh all around the character.
And then convert one item to accessory (or delete it) and ALL the body mesh becomes un-hidden.

Not to mention there is a constant conflict between 3 types of hide body mesh (auto, manual per cloth and manual body mesh hiding),
which could create a mess in iClone and requires complete reset of hide and conform.

Bottom line - the mesh hiding routine is due to overhaul.