Duplicate TUs created when making corrections in Editor mode

Question

I know that this issue was raised a couple of years ago here but it doesn't seem to have been resolved and I'm not sure it's even the same problem as the one I have been having for a while having. 
 Here goes: I have started a project as "Translate single document" and I have created a TM specifically for that document. After translating a segment, I confirm it, it updates my specific TM, and I move on to the next segment. Upon completing the document, I go back to the beginning and revise what I have done. If I make a correction, and then confirm the corrected segment, I end up with two TUs: one with the corrected text (with CM in green next to it) and another with the old text with a 100% match. I would have thought that the old text would be overwritten. 
 What am I doing wrong? Any ideas? 
 
 Thanks in advance

Stepan Konev · Answer

Any news? I experience the same issue now. Single TM, single user, single file, the entire event of 3 actions took 20 seconds (1. confirm, 2. go to next+confirm, 3. go back+remove+confirm)... 
 When checking if the Bilingual Excel char limit mechanism works properly, I copied and pasted my translation several times deliberately to exceed 255 char limit. Then I confirmed it, moved to the next segment automatically as designed, then returned to that segment again in order to remove the superfluous text, and finally confirmed it as it is supposed to be. Here is what I got: 
 Two 99% translations for the same segment. 
 After fiddling with it a while, I noticed that this only happens when I press 'Undo'. When I delete a portion of text with the 'Delete' key, confirmation just overwrites the segment. But when [after a first confirmation] I delete the same portion of text with the 'Undo' ctrl+z keys, Trados adds another instance after a second confirmation. It seems to me this behavior is caused by using the Undo command in the segment you are editing at the moment.

Trados Studio > 1. Trados Studio

Duplicate TUs created when making corrections in Editor mode