Password min. Length

I can't set in "password policy" minimum lenght. When I try to set min password lenght to 6 and press ok, it changes back to 8, that doesn't make any sense.
Even here is written "The optimum value of minimum Password length is 6 to 8 characters length.", and even when I put 0 it say that I need to type value from 1 to 60. But any value I put here it changes back to 8 when I click ok.