Hint brushes stop/detonate projectiles (latest svn).
Test: load frankishtower15 or frankishtowerctf16, the trees are encased in hintbrushes, you shoot them and the projectile explodes at the edge of the hint brush.

Btw, this is on a server with:
g_antilag_bullets 0

i am not sure wether this is due to hint brushes, but on Mentalspace there is similiar 'invisible walls' stopping bullets/laser at/on/below the moving center top platform ..

Fixed in svn..