Hi Crusoe, previously there could sometimes be a problem when unioning a big batch of things where a bunch of separate small pieces were being unioned on to one larger piece.

If the internal ordering happened that many of the small pieces (which do not intersect one another) were unioned together first into a bunch of little separate volumes, before they were intersected with larger piece that actually intersects them all, that could be buggy. When you do them one-by-one it avoids this problem since only an intersecting pair is processed.

One of the changes for the Nov-21 v2 beta was an improvement of the internal sorting for how a larger batch of small objects being unioned is handled, I think it should pretty well solve this problem area.

Also in the Nov-21 v2 beta was a bug fix for meshing where there could be some skinny cracks when 2 adjacent surfaces had UV quad gridding that was very close to being aligned with one another but not quite. It fixes the bug that was reported here by PaQ:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2091.1

I can't be sure if that fixes the bugs you ran into, because I don't have any examples of that from you but it sounds pretty similar.

If you run into it again, please send me the file if possible so I can reproduce the problem over here and work on fixing it. Otherwise it is very difficult for me to work on a fix if I don't have a repro case for the problem.

- Michael