UDB UART errors

Hi,

I'm using a UDB UART, and it's sometimes producing errors, despite the input signal looking well within spec. Am I doing something wrong?

I have two PSoC4s: one is transmitting "BlahblahHello!", and one is receiving. The receiving one has two outputs for debugging: 

1. A copy of the input digital signal, so I can check that it's getting a good waveform.
2. Re-transmitted bytes, so I can check that the UART us correctly interpreting the incoming signal.

The baud rate is 2Mbaud, using a 16MHz input clock on the UART component. Most of the time the UART works fine, but sometimes it seems to generate an error, and then loose synchronisation for the rest of the string.

The obvious cause would be that the transmitter and receiver have very slightly different clock frequencies. But I have checked their clocks using a 1MHz output from each using a PWM component. Their clocks differ by less than 0.1%. Am I doing something wrong? Is there anything I can do to reduce the error rate?

Hugo