Option autoconf option --debug no longer working

Dear autoconf maintainers,

when trying to port another piece of software to use autoconf 2.71 I noticed a problem I wanted to debug with the autoreconf --debug option. But it seems autoconf now deletes the temporary files in all paths.

While the 2.69 version I'm currently using preserves files in /tmp, when swapping the PATH to use autoconf 2.71, autoconf always unlinks the files there (and removes the temporary directory) as verified with strace -f -e rmdir,unlink on Linux x86_64.

I tried

autoconf --debug --verbose

in a minimal autoconf directory like this:

$ autoconf --debug --verbose 2>&1 | grep /tmp
autom4te: formatting traces for `/tmp/am4tYtdOcp/dependencies': include, m4_include
autom4te: formatting traces for `/tmp/am4tYtdOcp/warnings': _m4_warn
autom4te: reading /tmp/am4tYtdOcp/warnings
$ ls /tmp/am4tYtdOcp
dependencies  traces.m4  warnings
$ module load autoconf-2.71-gcc-6.3.0-rj5ute2
$ autoconf --debug --verbose 2>&1 | grep /tmp
autom4te: formatting traces for '/tmp/am4toeE5oa/warnings': _m4_warn
autom4te: reading /tmp/am4toeE5oa/warnings
autom4te: formatting traces for '/tmp/am4toeE5oa/patterns': m4_pattern_allow, m4_pattern_forbid
$ ls /tmp/am4toeE5oa/
ls: cannot access '/tmp/am4toeE5oa/': No such file or directory
$ cat configure.ac
AC_INIT([hello], [1.0])
AC_CONFIG_AUX_DIR([build-aux])
AC_OUTPUT
$  strace -f -e rmdir,unlink autoconf --debug --verbose 2>&1 | grep -E 'unlink|rmdir|/tmp'
autom4te: formatting traces for '/tmp/am4tciBmIE/dependencies': include, m4_include
autom4te: formatting traces for '/tmp/am4tciBmIE/warnings': _m4_warn
autom4te: reading /tmp/am4tciBmIE/warnings
unlink("traces.m4")                     = 0
unlink("dependencies")                  = 0
unlink("warnings")                      = 0
rmdir("/tmp/am4tciBmIE")                = 0
$  ls /tmp/am4tciBmIE
ls: cannot access '/tmp/am4tciBmIE': No such file or directory

Kind regards,
Thomas