XMC2go UART slipped multiple characters problem.

I applied it to flush TxFIFO in Dave, and I also tried to flush TxFIFO&RxFIFO in the computer GUI (MFC) with the function called PurgeComm(m_hComm, PURGE_ABORT|PURGE_RXCLEAR),
but the problem still happens..
In debug mode of Dave, everything are fine Rx&Tx, but in MFC debug mode, I found a pattern before the problem showed up.
Before the problem happened, when wByte (sending buffer from GUI) sent "012345", for example, then rByte (receiving buffer from Kit) received "" (empty string),
and then the slipped character problem showed up again.

Could you give me any other advice? The way you gave me was helpful, but I still couldn't solve the problem...

Regards
Sean