Followup -- The issue seems to have been resolved. I'm not sure how (neither Android BoxCryptor nor FolderSync seems to have updated in the interim); perhaps when I was having the problem it was because the text editor hadn't properly saved the file so that it was closed out and re-encrypted. In any case, I've done a few tests (open a file from Android BoxCryptor into a text editor program, make changes, save, close the text editor, close Android BoxCryptor, FolderSync, and check the DropBox copy on my desktop BoxCryptor, getting the expected result of the modified file showing up).