In my company, we translate a lot of similar documents at the same time, meaning that mistakes can slip into other documents before they are corrected in the documents they originally occurred in. It is difficult to prevent this from happening; the “Always overwrite existing translation” function of the pre-translate cannot, unfortunately, be trusted to leave other segments (such as segments with more than one 100% match) alone.

There appears to be no way of knowing if a translation has been changed in the TM since the document was translated. To find these "Different target in translation memory" segments, you would need to click through every segment in the document.

A solution could be to incorporate a warning into the QA checker which informs the translator that his/her translation does not correspond to the translation in the TM. This would be a very useful resource and play a major part in improving translation quality.