False duplicates

Hello all,
I experience a strange behavior in DT Pro since about end of August 2017. I frequently send invoices to customers, partly these invoices are made with Excel, partly with Word.
The workflow is simple: duplicate the Excel file and fill in the customers address, invoice number etc.

Since end of August the so modified Excel files are marked as duplicate (not the Word-files, only Excel is affected! - see screenshot: invoices number 646ff). Can anyone give me a hint to get back the former (and correct) behavior?
Bildschirmfoto 2017-09-09 um 10.35.52.png

What version of DEVONthink are you running?

I actually run Version 2.9.15

There currently is an issue with some Office files that may be causing this. It should be fixed in the maintenance release.