Hope this is the right place to post.
I just found what looks like a bug.
I'm encountering a strange building behavior in the following case (I attached FCstd file as it would probably be easier to figure out) :
*1) I created a vertical (Z) lofted profile in a pad => OK
*2) I added a round pocket going through the whole part horizontally (X) => OK
*3) I set the previous pocket to (polar) repeat at an angle of 90° (Y) => Ouch
=> A bunch of surfaces (no thickness walls) appears where the pockets cross inside the part (and where I expect a complete void)
* I tried replacing the polar repeat by a new pocket => no bug
* I tried the same polar repeating but applied inside a box created from a cube => no bug
I run Freecad 0.18 rev. 15159 installed from PPA on a up-to-date Kubuntu 18.04.
Hope this helps.