Keys not retained in backups but still listed in keys menu

When restoring an iOS device from a backup, all ssh private keys are lost.

They will still be listed in the keys menu, but they won’t work for authentication and attempting to copy the private key causes a crash.

My guess as to the intended behaviour goes two ways. Either:
1) private keys are retained in backup, can then be used as usual, or
2) private keys are not retained, delete them from the keys menu.

Details:
* iPhone 8 Plus, iOS 11.1b2
* Using the App Store version of Blink

Reproduce the issue by restoring an iOS device from a backup, then inspect the keys menu and the private-key copy flow described in the report. Done means restored keys behave consistently with the chosen backup policy, and missing private keys are not left listed or able to trigger a crash.

Written by the indexing model from the issue text.