In my recent post about SDL Studio, CU8 and a conflict regarding the "Update Translation Memory" batch task and "Add as New Translation" function (Ctrl+Shift+U), I wrote about the new default setting in the "Update Translation Memory" batch task: "Overwrite existing translation units". If you haven't read it yet, please start there to fully understand the situation. New default setting Unfortunately, the old behavior of Studio of only overwriting the existing translation unit (TU), as Ctrl+Enter would do in the Editor, has not been reintroduced as a batch task option yet: in CU10, the default setting has been changed to "Add new translation units".
The good thing is that you cannot erase any TUs from your translation memory (TM) anymore; the bad thing is that the batch task will systematically create a duplicate TU as soon as the target text has been changed without a Ctrl+Enter validation in the translation editor, for example while doing a review in Microsoft Word or an offline review in SDL Studio. "The overwrite option is fine for me" I have heard from many users that the "overwrite" setting was a good thing for them and their translation projects: if an unwanted duplicate TU has been added during the translation process, the batch task deletes it as well as all other TU with the same source and saves only one occurrence-- the (last) one found in the sdlxliff.
To use this "overwrite" option with CU8 and CU9, it was not necessary to change anything in the project templates.
Now, as the default setting has been changed in CU10, it is necessary to select the "overwrite" option explicitly in all templates and running projects. Running the batch task with CU10 without having made such changes will use the "Add new translation units" and new duplicate TUs will be created. 
In such a scenario, it is fortunately possible to delete immediately the created duplicates just by running the batch task again with the "overwrite" setting. All added TUs will be deleted and replaced by the (last) TU found in the sdlxliff file.