Failure in test 'amp-escape'

On Debian unstable, I'm seeing this error in the sed testsuite:

  make[4]: Entering directory `/devel/stefano/src/gnu/sed/testsuite'
  LC_ALL=C  ../sed/sed -f ./amp-escape.sed \
      < ./amp-escape.inp | LC_ALL=C tr -d \\r > amp-escape.out
  /bin/sh: ./amp-escape.inp: No such file or directory
  cmp ./amp-escape.good amp-escape.out
  cmp: ./amp-escape.good: No such file or directory
  make[4]: *** [amp-escape] Error 2
  make[4]: Leaving directory `/devel/stefano/src/gnu/sed/testsuite'

So far, this only happens in a git checkout bootstrapped with either
Automake 1.12.4 or Automake 1.13, but not in the 4.2.2 release tarball.
I've not investigated the issue any further for the moment.

Regards,
  Stefano