In the current implementation of QLowEnergyController (bluez) you cannot connect to an iPad (iOS 8) longer than 30 seconds.
After connecting to the iPad as peripheral, it sends requests to the central (QLowEnergyController) that will be ignored. According to the bluetooth ATT specification, if a request is not responded in between 30 seconds, the connection shall be closed.
To respond appropriate, the QLowEnergyController should answer with a "Request Not Supported" message.
I have observed this behavior with the bluez implementation of QLowEnergyController, but the other implementations maybe affected as well.