Hi, I had a very strange situation just now which I'm documenting here in case it happens to anyone else. I have a fairly complex object that I was trying to add another object to. They are both solids, and they overlap considerably. I called them bodyA and flangeA. I also have very similar objects, bodyB and flangeB which I was able to union just fine. At one point I was able to union the A pair successfully, but undid it because I wasn't ready. Later, after making a lot of changes to *other* objects in the same file, but not these two, when I tried to union, bodyA was deleted and only flangeA remained. This behavior persisted through closing and reopening the file, making a new file and deleting all the other objects, quitting and restarting MoI, and tweaking flangeA slightly in a way I could revert after the union.

While constructing a file, noUnion.3dm, to attach to a forum post asking for help, I tried the union once more. As happens often, when I click on the Boolean button, the Diff option comes up selected. Without thinking, I checked Keep Objects, which had been unchecked before. I then realized that I wanted to union instead, just to verify that the file I was sending had the problem. This time the union succeeded. I tried in my original file, and the union succeeded. I tried unchecking Keep Objects again, but now the union continues to succeed. Apparently there is some bug where the program can get into a state that the Keep Objects flag on Diff affects Union, but I don't have any idea how it got there.

Possibly this will help someone else who may have this problem. I was tearing my hair out for several hours trying to figure it out or work around it. Michael if you would like the file I was working with I have it saved, but it works now...

Rachel