[development] It's possible create alias with same name as system path?

Hi, I have tried create alias for user/1 - i use node which is system path and it's work. Then i try successfully replaced system path admin/build/path/list to user/1/edit alias and now if i clik on menu item with admin/build/path/list i get user/1/edit page. I try make vanity url module (user has select his own url alias for user/[uid]) and this is strange behavior for me. There is possibility for user overide some of system drupal paths. It is this bug or feature? Thanks, Juraj Chlebec aka Havran