How to reproduce (Note that the printf does not add a newline at EOF) :
  printf 'OEQA_REPRODUCIBLE_TEST_TARGET = "bash"' >> conf/local.conf
  oe-selftest -r reproducible.ReproducibleTests

This fails because the generated build-st/conf/local.conf used by the reproducible test ends with:
  OEQA_REPRODUCIBLE_TEST_TARGET = "bash"SSTATE_DIR ?= "/home/yocon/yocto/sstate-cache"
  
  #include added by oe-selftest
  include machine.inc
  include selftest.inc

To fix this: "oe-selftest -r reproducible.ReproducibleTests" needs to add a newline before adding lines. But beware, we don't want too much of double spaced variables.