OTM with 0.505 delta

I'm reviewing option data exported from TWS, the following two options make me confused.

SPY: $246.64
SPY Apr09'20 247 Call
Delta: 0.505

SPY Apr09'20 247 PUT
Delta -0.495

I always thought an OTM option's delta is less than 0.5, and an ITM option's delta is bigger than 0.5, but it's not the case here. Did I misunderstand something?

 

When volatility is high, deltas are higher to the call. Intuitively, imagine that volatility is infinite - while that means the stock can go very high, it still can't be below zero.

 

Unless you're IB and calculating the margins for selling puts, apparently.

 

Lemme guess, they charge you more than the strike price as margin?

 

Not me, I moved long ago, but some discussion at https://www.elitetrader.com/et/threads/short-svxy-put-margin-logic.342291/