Why am I losing data when using a vxWorks pipe?

Init()
{
   fd = open("/pipe/mydev", O_RDWR, 0777);
...
}

taskRx()
{
   ...
   len = read(fd, rxbuf, MAX_RX_LEN);
   ...
}
taskTx()
{
   ...
   len = write(fd, txbuf, txLen);
   ...
}