Static passkey and MITM

Question

I am trying to add a static passkey to my peripheral and protect from MITM. I tried the example nRF51-ble-app-uart-static-passkey but it doesn't seem to work correctly. 
 I am using: 
 
 PCA10001 board 
 S110 v7.3.0 
 nRF51 SDK 6.1 
 nRF Master Control Panel 
 
 First, bonding the device still works without a passkey. I have set sec_param.io_caps = BLE_GAP_IO_CAPS_DISPLAY_ONLY and sec_param.mitm = 1 . Looks like it is still using the Just Works, instead of the passkey authentication? What am I missing? Shouldn't I now have to enter the static passkey I set in my peripheral on the phone when I try to bond? 
 Second, I don't get any data on the characteristics. Only when I use BLE_GAP_CONN_SEC_MODE_SET_ENC_NO_MITM I can send and receive data. As long as I use BLE_GAP_CONN_SEC_MODE_SET_ENC_WITH_MITM I don't get anything, neither read nor write. I suppose this is because the bonding is still using the unauthenticated method instead of the authenticated?

Dominik · Accepted Answer

It seems the problem was indeed my phone and not the software. I was using an HTC M8, with stock rom, and apparently they botched up. I now tried it on two other phones and it is working properly, meaning I do get a popup where I have to enter the static pin, and only if I enter the correct pin bonding succeeds. 
 On the M8 on the other hand, bonding succeeds without any input ...