This is rediculous, 4 years and no solution?? Seems like Apple is intentionally screwing business users that don't use proprietary stuff like MS Exchange or Cisco VPN. The generic L2TP VPN functionality is similarly crippled (VPN does not persist across locks requiring manually enabling it EVERY TIME you unlock and making it useless). People have been complaining about that for years too, and I can only conclude it's by design.
If you're a hipster and need to Facebook and twitter all's fine. If you are a business and want to pay through the nose for an Exchange server license and Cisco hardware for reliable VPN it's all dandy too.
But if you would like to use your rediculously expensive phone to use open standards, forget it. They implement it so they can claim support in the specs, but intentionally cripple it so it's basically useless for an advanced user. Surely this is to push people to MS and Cisco products (in return for a kickback or for instance usage of Cisco's trademark 'ios').
I for one will be returning all 80 iPhones we bought for our employees since I consider them defective, and there isn't a hint of a fix.