Bulk write fails on OSX but works on Linux

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Hello,

I'm trying to do some bulk IO with a custom USB device on OSX and fail 
miserably. This is the small source code which just tries to write a few 
bytes to a bulk endpoint:

#include <stdio.h>
#include <libusb-1.0/libusb.h>

int main()
{
     libusb_context *ctx;
     libusb_device_handle *handle;

     libusb_init(&ctx);
     libusb_set_debug(ctx, 3);
     handle = libusb_open_device_with_vid_pid(ctx, 0x16c0, 0x05dc);
     libusb_set_configuration(handle, 1);
     libusb_claim_interface(handle, 0);

     unsigned char *write_data = "\1Test\0";
     int written;
     if (libusb_bulk_transfer(handle, 0x04, write_data, 6, &written, 2000))
     {
         printf("write failed\n");
         return 1;
     }
     printf("%i bytes written\n", written);

     libusb_release_interface(handle, 0);
     libusb_close(handle);
     libusb_exit(ctx);
     return 0;
}

The program runs fine on Linux but when I try it on OSX (with the same 
USB device) then the libusb_bulk_transfer call fails with 
LIBUSB_ERROR_PIPE and the following debug messages:

libusb: 0.533303 info [darwin_open] device open for access
libusb: 0.551238 info [get_endpoints] building table of endpoints.
libusb: 0.551277 info [get_endpoints] interface: 0 pipe 1: dir: 1 number: 4
libusb: 0.551287 info [get_endpoints] interface: 0 pipe 2: dir: 0 number: 4
libusb: 0.551323 info [darwin_claim_interface] interface opened
libusb: 0.551339 info [ep_to_pipeRef] converting ep address 0x04 to 
pipeRef and interface
libusb: 0.551344 info [ep_to_pipeRef] pipe 2 on interface 0 matches
libusb: 0.551495 info [darwin_async_io_callback] an async io operation 
has completed
libusb: 0.551527 info [op_handle_events] checking fd 4 with revents = 0
libusb: 0.551535 info [op_handle_events] checking fd 6 with revents = 1
libusb: 0.551544 info [darwin_handle_callback] handling bulk completion 
with kernel status -536854449
libusb: 0.551550 warning [darwin_transfer_status] transfer error: pipe 
is stalled

I'm confused. If I'm doing something wrong here or when the USB device 
is doing something wrong then why does it work on Linux? Is there 
anything wrong in my code which can cause this error only on OSX? On OSX 
I'm using libusb-1.0.9 while on Linux I'm using the libusb package 
shipped with Ubuntu. I also tried using the old libusb-0.1.12. Same 
problem: Works on Linux, fails on OSX. Any help is highly appreciated.

-- 
Bye, K <http://www.ailis.de/~k/>
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