Nios-II SOPC UART delivers wrong bytes

We are finding the same or a similar problem. We have 2 devices, we program one to just transmit. Every four seconds we send a blast of data 0-255. If we enable Rx and listen to ourself on that device, we hear all 256 characters nice and clean. We then plug into a second device and enable it to Rx. We loose about one byte in 16. We have tried blocking, non-blocking, read only, read write, disabling the transmitter. We have tried open(), fopen(), we have used getc() and read(), and more.