Harald Braun 

I guess you mean something like this pair:

Source & target are the same, only the tag IDs differ.  In this situation it probably doesn't make any difference which one you delete... other than each one may provide a Context Match in a different situation.  So if you remove one it's possible you may only get a 100% match for some situations and yet a CM for another.  But if that doesn't matter, then you can remove either of them.

The reason you can do this is because the TM doesn't hold tag detail, it only holds a placeholder.  That placeholder is replaced by detail in the editor because the detail comes with the source file.  For example:

I have three different files, a DOCX, HTML and XML.  The content of each tag is different, but when I add the first one to my TM I get a match for the other two as well.  I get a CM as there was only one sentence in this simple example so the context is exactly the same in each case.

If I select a different entry the TM results window fills my tags with the content of the source:

and...

If I select TagID mode I will see different TagIDs in the TM results window, but only in the source.  The end resut will be to make sure that the tags contain the correct content for the file I'm translating.

This an inherent ability in Trados Studio to ensure you get the maximum possible leverage from your TM.

Hope that helps?

Thanks for the fast answer, that sounds really good. 
I will talk with my colleagues and we will try your solution in the next weeks.