This jar file might fix *some* of the DMI issues:
Can't download it until the next time I'm on real internet, but I've bookmarked the page to check it out when I am (might be a month)
Managed to download the thing (in chunks, using a download manager... ugh), and it looks like you cleared up all of the drawing issues. Good stuff, I'll definitely be keeping up with this project as it progresses, big stuff like details about the tile the mouse is over and an instance editor would really put this thing into the usable category and I anxiously await those features.
There is basic instance editing

Above the object tree, there is an "Instances" tab that lets you select instances (If you want to know the variables, hover over it with your mouse and a tooltip should show the variables in /blah/blah{a = 1; c = "d"} format

Right-clicking is a thing, not sure if you didn't try it or it simply doesn't work on your system.
I don't mean seeing what's on the tile, I mean showing basic information about the tile as you mouse over it, such as coordinates, little things the DM map editor has that make the job easier.
Tried to load up one of Severed World's maps:

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