Not just today, and not just VWO. I have noticed this phenomenon with a variety of ETFs, including those other than Vanguard. The range usually gets increasingly wider as you get further into after-hours trading. My guess has always been that it's their way of discouraging after-hours trading of their funds.
When I used to trade VTI, VEU, VEA, VWO, etc., I would set limit orders around the previous day's closing price to avoid an after-hours market order at a stupid premium. From what I experienced, it's virtually impossible to buy or sell these ETFs outside of 9:30 - 4:00 unless you hate money.