Hello,
I'm one of the Slovakian Lego fan but I'll save this for another topic specialized for it...
I was trying add some parts behind the part#: 30601, Rear, Motor Block in LDD 4.1.8 and I think i've found a bug.
If you try put two 30601 with back together as in pic1, it's impossible but if you make a "small wall" behind it like in pic2, it's possible but you can't add block into the hole.
Geometry bug?
I hope this isn't repost because i didn't found this bug in few previous pages.