Is that the one where at some point more minaturization you have, the larger the components become?
That's not a bug, just the way it is. Part of a component's size is based on the hull's total size, so miniturization only really benefits the part of a components size that is fixed.
The only real 'bug' is that due to rounding+sizemods working in perfect disharmony, you can sometimes end up with components growing by more than the hull's capacity did, meaning that some existing designs can become impossible to build (though I've not encountered this myself, I have heard reports of it).
Now, one can argue that sizemods should ignore miniturization and only be based on the base capacity of a hull, though that may swing things the other way and make miniturization too powerful--it'd need some testing to figure that out. And the rounding issues can be solved by simply multiplying all sizes by 10 or 100.