nativecall oddness

p6-lmdb $ ./foo2.pl6 
Segmentation fault (core dumped)
p6-lmdb $ ./foo.pl6 
LMDB 0.9.70: (December 19, 2015)

p6-lmdb $ ./foo3.pl6 
LMDB 0.9.70: (December 19, 2015)
p6-lmdb $ ./foo4.pl6 
Segmentation fault (core dumped)

#foo.pl6
#!/usr/bin/env perl6
use NativeCall;

#map mdb functions
sub mdb_version() returns Str is native('./lmdb') { ... }
#sub mdb_version() returns Str is native('./lmdb') { ... }
#sub mdb_version() returns Str is native('./lmdb') { * }
#sub mdb_version() returns Str is native('./lmdb') { ... }
say mdb_version;


#foo2.pl6
#!/usr/bin/env perl6
use NativeCall;

#map mdb functions
#sub mdb_version() returns Str is native('./lmdb') { ... }
#sub mdb_version() returns Str is native('./lmdb') { ... }
#sub mdb_version() returns Str is native('./lmdb') { * }
sub mdb_version() returns Str is native('./lmdb') { ... }
say mdb_version;

#foo3.pl6
#!/usr/bin/env perl6
use NativeCall;

#map mdb functions
#sub mdb_version() returns Str is native('./lmdb') { ... }
#sub mdb_version() returns Str is native('./lmdb') { ... }
sub mdb_version() returns Str is native('./lmdb') { * }
#sub mdb_version() returns Str is native('./lmdb') { ... }
say mdb_version;

$foo4.pl6
#!/usr/bin/env perl6
use NativeCall;

#map mdb functions
#sub mdb_version() returns Str is native('./lmdb') { ... }
#sub mdb_version() returns Str is native('./lmdb') { ... }
#sub mdb_version() returns Str is native('./lmdb') { ... }
sub mdb_version() returns Str is native('./lmdb') { * }
say mdb_version;