Hi Val, it sounds similar to the steps reported here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2177.1

But yeah there was a bug in the previous Nov-21 beta with mirrored objects having a kind of messed up inside/outside directions. Later in that thread there is a patch attached to a post that you can download and apply to that previous beta to fix it up in that version.

But this should also be fixed in the new Jan-19 beta that was just released:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2333.1

Can you repeat this problem in the new beta or is it fixed for you with this new beta release?

- Michael

yep! it works without problems :)
thanks

This bug is still present to some degree in the January beta.

I attempted a boolean union between an object and a mirrored object on a model, but the regular object just disappeared. Fortunately the object was symmetrical, so I was able to solve it by deleting the mirrored object, copying the original object and rotating it into place.

Hi LOTRJ, there are also some other things that can cause stuff similar to what you describe, such as if the objects involved in the booleans are open surfaces instead of closed solids.

I can't really tell if it is another instance of that previous bug or not without an example, can you please post the .3dm model file of the instance that you ran across so I can check it out?

If you don't want to post it in public here, you can also send it privately to me at moi@moi3d.com .

That would help me more definitely determine what was happening there.

- Michael