I tried the customer service chat but the person there couldn't tell me why it was this way. He asked me to send a support ticket. Which I did a moment ago.
They responded. It was a glitch for Canadain accounts. They didn't know that the margin for VXX/UVXY shares were not increased as well up here.... Here it is. Dear Brennen, Thank you for pointing out this margin error effecting our Canadian accounts. We are currently working to increase the margin requirement to the correct level of 75% for Initial margin and 50% for maintenance margin for the VXX underlying. Regards,
Experimentally, it appears to me that Interactive Brokers's new volatility exchange traded product margining at least sometimes requires much more margin for a protective call (short underlying + long call) on a long volatility ETP than a long put with the same expiration and strike, even though the exposure is basically the same. I am a bit surprised by this because IB normally explicitly recognizes a protective call combination and offers pretty good margin for it.