Native call expected return type with CArray representation, but got a VMArray

Example.pl6

use v6;
use NativeCall;

# Needed bindings.
our sub fopen(Str $filename, Str $mode) returns OpaquePointer is 
native() { ... }
our sub close(OpaquePointer $handle) is native() { ... }

# Bingings to bzip2(only needed parts).
our sub BZ2_bzWriteOpen(Pointer[int32], OpaquePointer, int32, int32, int32) returns OpaquePointer is native("/lib/libbz2.so.1") is export { * }
our sub BZ2_bzWrite(Pointer[int32], OpaquePointer, CArray[uint8], int32) is native("/lib/libbz2.so.1") is export { * }

# Code for testing.
my $text = CArray[uint8].new;
$text = "Test string.\n".encode;
my $filename = fopen("/tmp/test.bz2", "wb");
my $bzerror = Pointer[int32];
my $bz = BZ2_bzWriteOpen($bzerror, $filename, 1, 1, 0);
BZ2_bzWrite($bzerror, $bz, $text, 15); # Obviously error is here.

close($filename);

# C headers:
#BZ_EXTERN BZFILE* BZ_API(BZ2_bzWriteOpen) ( // It'll be just "BZ2_bzWriteOpen" 
#      int*  bzerror,      
#      FILE* f, 
#      int   blockSize100k, 
#      int   verbosity, 
#      int   workFactor 
#   );

#BZ_EXTERN void BZ_API(BZ2_bzWrite) ( 
#      int*    bzerror, 
#      BZFILE* b, 
#      void*   buf, 
#      int     len 
#   );

use v6;
use NativeCall;

# Needed bindings.
our sub fopen(Str $filename, Str $mode) returns OpaquePointer is native() { ... }
our sub close(OpaquePointer $handle) is native() { ... }

# Bingings to bzip2(only needed parts).
our sub BZ2_bzWriteOpen(int32 is rw, OpaquePointer, int32, int32, int32) returns OpaquePointer is native("bz2", v1) is export { * }
our sub BZ2_bzWrite(int32 is rw, OpaquePointer, CArray[uint8], int32) is native("bz2", v1) is export { * }

# Code for testing.

# You need to first encode the string to a Buf and then copy the
# element of the Buf to the new CArray
my $text = "Test string.\n";
my $t_buffer = $text.encode;
my $buff = CArray[uint8].new;
$buff[$_] = $t_buffer[$_] for ^$t_buffer.elems;
my $filename = fopen("/tmp/test.bz2", "wb");
my int32 $bzerror;
my $bz = BZ2_bzWriteOpen($bzerror, $filename, 1, 1, 0);
say $bzerror;

# use the length of the buffer as the length
BZ2_bzWrite($bzerror, $bz, $buff, $t_buffer.elems); # Obviously error is here.
say $bzerror;

close($filename);