Harrisburg Tradition?

According to Ursula's latest picture-filled EMail, it's a tradition in Harrisburg to trick-or-treat on the Thursday before Halloween. Weird. Why, I wondered. Surprisingly, Google (and I even tried Bing) is not much help on why it happens, although I did discover the how it happens:

Mayor Stephen R. Reed reminds city residents that Trick or Treat Night in Harrisburg and most of Dauphin County’s other municipalities will be held on Thursday, October 29, from 6:00 to 8:00 p.m. The date and time for the fun-filled evening is annually set by the Dauphin County Chiefs of Police Association.

The police decide!? That seems decidedly un-Halloweeny to me.