Release 1.1.0 is broken, but tests pass

This is very weird. Tests pass but not when Majic is used in another project.

I get test errors like this:

  6) test reads the cards in a given folder (Project.SomeTest)
     test/project/some_test.exs:7
     ** (EXIT from #PID<0.652.0>) {:error, {:unexpected_error, 8}}

19:52:55.662 [error] :gen_statem #PID<0.677.0> terminating
** (stop) {:error, {:unexpected_error, 8}}
    (stdlib 5.2.3) gen_statem.erl:1524: :gen_statem.loop_state_callback_result/11
    (stdlib 5.2.3) proc_lib.erl:241: :proc_lib.init_p_do_apply/3
Queue: [info: {#Port<0.37>, {:exit_status, 8}}]
Postponed: [{{:call, {#PID<0.668.0>, [:alias | #Reference<0.0.85507.3397650879.3987800065.21423>]}}, {:perform, "/tmp/image.jpg"}}]
19:52:55.663 [error] GenServer #PID<0.672.0> terminating
** (stop) {:error, {:unexpected_error, 8}}
Last message: {:EXIT, #PID<0.668.0>, {:error, {:unexpected_error, 8}}}

completely useless errors!

But when I revert the Makefile changes and rebuild Majic, it works again.