M L 

What do you mean by this?

M L said:

any changes that I make will be a second layer of tracked changes.

Normally the target is the translation of the source.  So when you open a file with Tracked Changes you can display these changes in the source so they are visible but you cannot transfer them to the target.  The only way to manage this is to translate the file as if the original before tracked changes is translated, then turn on tracked changes and make the changes.

I think translating an unfinished document is uncommon.  Most workflows normally make sure the document being translated is complete and approved before creating translations into multiple languages, otherwise you could end up having to change them all.

Every proofreading/editing job I've ever done (on a Word document or similar) has called for "Track changes" to be turned on.

In other words, the client wants the changes to be visible before final approval is given.

And in many cases (including a job I worked on today), the file I am editing already has tracked changes from a previous writer/editor.

If I were to edit the file directly in Word (or a similar program), this information about the edit history would not be erased – so why should it have to be erased in Trados?

M L 

M L said:

so why should it have to be erased in Trados?

As I said... Trados is a translation tool.  The appropriate process is to translate approved documents, not unapproved documents.  If you had a multilingual project that went into 40 languages and the source was unapproved, then once it was approved you would have to change all 40 translations.

M L said:

Every proofreading/editing job I've ever done (on a Word document or similar) has called for "Track changes" to be turned on.

ok - in Trados this task would normally be done on the bilingual file in Trados.  You open it for review and tracked changes are already on.  Every change you make is tracked so someone can proof your work and generate the finished targets.

It sounds as though you are taking a translated target files, and translating it into the same language in Trados just to proof it.  I can't think why else you would be copying source to target and being concerned that track changes were lost.  In this case why don't you just proof it in the final format if you don't have a bilingual file?  Maybe you are using Trados for something it was never intended to be used for?

Maybe I'm completely misunderstanding you!!!