Hi Metin,

> I've just tried to create something similar to your example above, but Boolean Union doesn't
> seem to work after selecting the bar and the outer shell of the cup-like solid.
>
> I've attached the MoI file.
>

I've been able to investigate the case you posted, and I've got it fixed up so it will work properly in the v3 final version.

It had to do with some additional processing happening with coincident surfaces (the 2 overlapping planes in your case here) that could end up making some intersection results outside of the subset area, confusing the boolean mechanism.

Thanks for posting the problem file!

- Michael