Props clip through each other

Is this supposed to happen, or is it just a bug?

Specifics?
Some props do collide with each other, the designer marks them as details, and they don’t collide with other details or the player.

Please show a video or screenshot of the bug.

Founded in 2004, Leakfree.org became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.