Hi Sagda, yes so like Pilou mentioned that boolean behavior is because the object isn't a closed solid. The booleans determine which pieces of objects to keep and which to discard based on what solid volume they are contained inside of. When the objects aren't solids that method can't be used and instead it work more like surface trimming.

There is a script you can set up which will highlight naked edges (edges that are not joined between 2 faces) here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2798.6

In your case here though it's hard to find them because they are very small and spread out in 3 areas:







It looks like it was probably caused by filleting having some difficulty in that spot. Probably the reason for filleting having difficulty there is the surfaces here aren't quite tangent to each other:








Things that are nearly smooth like that but off by just a few degrees tends to make things difficult for filleting. That's because if surfaces meet smoothly then the fillets generated along them will also meet smoothly but if there is a crease between surfaces, the fillet pieces don't naturally end and they have to be trimmed against each other and possibly a corner juncture patch put in, but these things are difficult to calculate when the angle deviation is very small.

It should probably be feasible to repair your object and get rid of the naked edges by some strategic untrimming and retrimming, I'll give that a try.

Also there are some tips for people coming from a poly modeling background here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

- Michael