When you select "Import Media" in a bin and the "Select files to Import" window shows up and start selecting the files that you would like to import, if you click on the "Options..." button to double check or change your import settings, Avid will forget what files you had selected for import. This happens to me most often when I go to import stills or motion graphics because I end up changing my import options after making a selection. I'll navigate to the location of the files, select the ones I want to import, then remember that I need to change the color levels to "Scale from full range to legal range" because I'm going to be importing RGB graphics/stills. When I click on "Options...", the "Select files to Import" window disappears. After changing the color levels and clicking "OK", the "Select files to Import" window reappears, but it has forgotten which files I have selected for import (and sometimes forgets the folder location entirely). Not a huge deal if you're only importing a couple of files, but if you've selected specific files out of a large amount of files in a folder it becomes a bigger problem.
This did not used to be the case. I believe it started happening when MC7 came out. I used to be able to select files for import, open up the options window and the "Select files to Import" window stayed up behind the options with the selected files highlighted.
I am on MC 8.5.3 on a 2010 Mac Pro running on Yosemite. This problem was also present when I was on MC7 and MC8.4 while on Mountain Lion.
Thank you!