nrf51.cpu -- clearing lockup after double fault

[atoncetti]

Running apache-mynewt-nimble/apps/bleprph app on a micro:bit v1 yields the following problem:

$ newt run myperiph 0
App image successfully generated: ...
Loading app image into slot 1  ...
; nrf51.cpu configure -event gdb-detach {if {[nrf51.cpu curstate] eq "halted"} resume;shutdown}
GNU gdb (GNU Arm Embedded Toolchain 10.3-2021.10) 10.2.90.20210621-git

--Type <RET> for more, q to quit, c to continue without paging--

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Reading symbols from ...
0xfffffffe in ?? ()
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0xfffffffe msp: 0xfffffffc
0xfffffffe in ?? ()
target halted due to debug-request, current mode: Thread 
xPSR: 0xc1000000 pc: 0xfffffffe msp: 0xfffffffc
(gdb) c
Continuing.
nrf51.cpu -- clearing lockup after double fault

Program received signal SIGINT, Interrupt.
0xfffffffe in ?? ()

Setup:

# target.yml
target.app: "@apache-mynewt-nimble/apps/bleprph"
target.bsp: "@apache-mynewt-core/hw/bsp/bbc_microbit"
target.build_profile: optimized

# syscfg.yml
syscfg.vals:
      LOG_LEVEL: 255
      BLE_LL_CFG_FEAT_LE_ENCRYPTION: 0
      BLE_SM_LEGACY: 0
      BLE_SM_SC: 0

# project.yml

...

repository.apache-mynewt-core:
    type: github
    vers: 0-dev
    user: apache
    repo: mynewt-core

The same problem occurs with other example apps.