Our application has a custom startup routine which loads a Project Manager which, among other things, presents a list of all Projects and, upon selection of a Project presents a list of Drawings in that project folder. Until about 3 years ago our app ran only in SDI mode. Our user base currently uses all versions of ACAD from 2002 through 2013 (the original app was written for ACAD Release 9). Support for MDI mode was added primarily because we were porting the app to Bricscad which only ran in MDI mode at that time.
The problem: Our startup routine works fine in SDI mode for all versions of ACAD and MDI mode for 2002 through 2007 plus 2011. It fails in MDI mode for 2008, 2009, 2010, 2012, and 2013. I suspect the solution is some sort of reactor, but I have zero experience with reactors (although I've written more than 20,000,000 million lines of AutoLisp code), so I'm not sure where to start.
One clue is that while the cursor is immediately available in SDI mode, it takes some time for it to become available in the troublesome versions in MDI mode. Any help would be appreciated.