Studio 2015 is creating duplicate TU's in target file rather than overwriting amended units, in Editor View. Any TM setting is being used.

I therefore end up with several target units including ones with minor errors in that I have since corrected, which is unhelpful. Project Settings are set to 'Merge translation units (recommended)'. I have not had this problem before. Current project uses 'Any TM' for a translation from FR to US English (the TM used is FR to UK English). I wonder if problem could be specific to the Any TM setting. Is there a way around this?