Is re-pairing necessary with MITM protection?

[Mateusz]

I am working on a peripheral. This peripheral is IO display only. On the other side, the central is keyboard + display. I have a single, custom service with a single characteristic. Said characteristic is readable and writable and requires both encryption and authentication. Pairing seems to work - I can read and write to it successfully.

However, with bonding enabled, once I re-connect and try to read or write to that characteristic, I get an "Insufficient Authentication (Error Code 0x05)" error.

Is this expected? When using MITM protection, does a central always need to re-pair?

[Mateusz]

According to a book "Getting Started With Bluetooth Energy" by Kevin Townsend & others, "Insufficient Authentication (...) denotes (...) that the link is encrypted, but the LTK used to perform the encryption procedure is not authenticated (generated with man-in-the-middle protection (...)) while the permissions required authenticated encryption".