Selecting multiple entities not working

I am using the free version of Draftsight 2018 SP2 x64 on a Windows 10 computer. About a week or so ago, I started having a problem with selecting multiple entities, for instance for a Copy or Move or Delete command. The program only keeps the last entity selected. I suspect I might have inadvertently changed a setting, as the issue only started happening recently. Any and all suggestions to fix this would be appreciated.