[bug-gawk] Function call bug in GNU Awk 3.1.6

[Louis Jean-Richard]

Here after a simplified down awk program that misbehaves:
    awk --version
    awk  '#
        function indexKey(data) {
            "echo \x22" "30c9a839" data "\x22" | getline key
            return substr(key, 1, 32)
            }
        BEGIN {
            TW = sprintf("%032d756f36b", 1357)
            TWK = indexKey(TW)
            #
            keyAAAA =  indexKey("AAAA-" TWK)
            keyBBBB =  indexKey("BBBB-" TWK)
            keyCCCC =  indexKey("CCCC-" TWK)

            print "AAAA  " keyAAAA
            print "AAAA- " indexKey("AAAA-23056")
            print "BBBB  " keyBBBB
            print "CCCC  " keyCCCC
            print "    The following four lines should be the same as the four preceding."
            print "AAAA  " indexKey("AAAA-" TWK)
            print "AAAA- " indexKey("AAAA-23056")
            print "BBBB  " indexKey("BBBB-" TWK)
            print "CCCC  " indexKey("CCCC-" TWK)
            }
        '

on my box with ubuntu this gives:

louis$ gawk_bug
GNU Awk 3.1.6
Copyright (C) 1989, 1991-2007 Free Software Foundation.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.

AAAA  30c9a839AAAA-30c9a83900000000000
AAAA- 30c9a839AAAA-23056
BBBB  30c9a839BBBB-30c9a83900000000000
CCCC  30c9a839CCCC-30c9a83900000000000
    The following four lines should be the same as the four preceding.
AAAA  30c9a839AAAA-23056
AAAA- 30c9a839AAAA-23056
BBBB  30c9a839AAAA-23056
CCCC  30c9a839AAAA-23056


This bug took half of my work day to pin down...

Sincerely

Louis Jean-Richard