sftp_write failure question

[reid.thompson@xxxxxxxxxxxxxxx]

with code of the format below ( pulled from the examples ) where source
is say 75MB in size.

...snip...
    while ((len = sftp_read(source, data, 4096)) > 0) {
        if (sftp_write(to, data, len) != len) {
            fprintf(stderr, "Error writing %d bytes: %s\n",
                    len, ssh_get_error(session));
            sftp_close(to);
            sftp_close(fichier);
            goto end;
        }
    }
...snip...

read/write will successfully transfer the complete file.

if the code is altered to 
                                                                     
...snip...
BUF_SIZE=xxxxx
char data[BUF_SIZE] = {0};
...
    while ((len = sftp_read(source, data, BUF_SIZE)) > 0) {
        if (sftp_write(to, data, len) != len) {
            fprintf(stderr, "Error writing %d bytes: %s\n",
                    len, ssh_get_error(session));
            sftp_close(to);
            sftp_close(fichier);
            goto end;
        }
    }
...snip...

read/write will succeed until the value of BUF_SIZE is set to 262120 or
greater.
at which point sftp_write will write BUF_SIZE and sftp_packet_read will
fail with "Received EOF while reading sftp packet size" and the SFTP
server will log a bad message error:
    "Jul 15 17:28:28 endpoint sftp-server[1537206]: error: bad message from 100.98.195.26 local user rthompso"

Is this expected/is this an internal limit to the amount that can be
written per invocation?
Is there a way to increase the amount of data that can be successfully
written per invocation?


Thanks,
Reid