A couple reasons for this of the top of my head;
-Occasionally they reorganize all the costume pieces, changing up their index values and such (or in a more extreme example, I believe they somewhat recently combined the 'masks with hair' options in with the general, as there was little difference between the two in the first place. Or moving tails to the bottom section rather than lumping them in with belts). Whenever this happens, it does not affect your costume out in the world, but open up the editor interface and suddenly things that are in conflict revert to a more default state. It does keep the colour selections, so all you have to do is re-find the correct costume pieces.
-Less likely but still possible is that some legacy costume parts have been removed, or certain combinations of parts is no longer allowed (STILL kicking myself for blindly customizing my fire blasts on one costume where I had the Magic Bolero+Wings 
) In these cases, you have to choose between editing the costume, or losing some parts that are no longer possible.
Keep in mind that in both cases, backing out of the editor instead of accepting changes will not alter your costume.
As for restoring the costume, your best bet is to take a screenshot or two of your costume, and then either set CoH to windowed mode and re-size so you have the screenshot and the editor in view, or just have both open and alt-tab between the two. (I often find this is also the best way to put enhancements back after a respec)
"My inner mind has become a reality-cracking overgod. He torments me! Help!"
Sorry if this question has been asked before. When I go to the tailor to edit my costume, some parts of it are already modified. I didn't make any changes yet just by opening the costume editor there are several charges made to the different body sections. Why is this happening and how do I stop it? Is there a way to get a list of what the options of a costume are called before editing? That way I know what they are so I can restore an altered costume.
Thanks in advance.