For documentation porpoises and to help a future troubled soul with a similar ugly bug. This is the walk around I used to handle the problem.

I still think there is something buggy in xubuntu, that causes the WINCH signals to pile up if they come too quick one after another, so I had to introduce a mechanism to process one by one and give it enough time to each process to finish

#$SIG{'WINCH'} = sub {
#    if (!$CONNECTED) {
#        return 1;
#    }
#    while (!$EXP->slave) {
#        select(undef, undef, undef, 0.1);
#    };
#    $EXP->slave->clone_winsize_from(\*STDIN);
#    kill 'WINCH'=>$EXP->pid if $EXP->pid;
#};

sub winch {
    $SIG{'WINCH'} = undef;
    select(undef, undef, undef, 0.2);
    while (!$EXP->slave) {
        select(undef, undef, undef, 0.1);
    };
    $EXP->slave->clone_winsize_from(\*STDIN);
    kill 'WINCH'=>$EXP->pid if $EXP->pid;
    $SIG{'WINCH'} = \&winch;
    return 1;
}
$SIG{'WINCH'} = \&winch;
[download]