One of the problems a clean install of 8.1 didn't sole is: TWINS.
For each image I import into the catalog, two will show up. One is the intended importee, the second one is an image that had been deleted from catalog and disk a long time ago. Both share the same file name.
Each importee gets it's individual twin (no twin sharing), although the same images that show up as twins in one import session may and will show up as twins again in the next import session.
It drives me nuts!

Technical stuff: Mac Pro 1.1, which cannot run an OS later than 10.7. Since C1 8.x requires OSX10.9 or later, I have the C1 Windows version and run it on Windows 8.1 through Parallels. Not sure if this could be a factor.
Any suggestion how to get rid of those twins greatly appreciated.