I suddenly noticed today that Draftsight couldn't open multiple documents at the same time.  I'm not exactly sure when it "broke", but I am sure it had been working on my Mac earlier this year. There isn't much information on this online, but a little digging led me to the SDI / MDI mode setting (Single Document Interface, Multiple Document Interface).  I found this flag in the Options -> System Options -> General settings, but you can't change it.  It was permanently set to SDI mode in my installation.  After poking around some, I found the setting in this XML file:

~/Library/Preferences/DraftSight/13.0.2/Profiles/__unnamed profile__/profile.xml

The changed the setting as follows:

WAS:  

IS:  

Once I made this change, it works again in MDI mode as expected.

I did a test, and installed version 2016 SP2 on a Windows machine, and this same setting is available and works just fine from the General options menu, unlike the Mac OS X version.  I couldn't test on my Linux system (long story, in 2014, I intentionally installed 32-bit Linux specifically because Draftsight wasn't available for 64-bit systems. When they came out with 64-bit version, they dropped 32-bit completely.  I therefore haven't updated my Linux version of Draftsight since the 2014 release, or else I'd have to reinstall my whole OS). 

I posted this in order to

• • help anyone else who has this problem, and
  • suggestion the UI be modified to permit Mac users to toggle the SDI setting option.