From the problem report that you submitted to Triscend SupportCenter, I see that you are using FastChip 2.4.0.

After the FastChip 2.4.0 release, we discovered some anomolies with the UART receiver when used with a FIFO. There is a patch for the release at the following link.
ftp://ftp.triscend.com/fc240/FastChip2.4.0patch7-15-02.exe

The problem is also described in the FastChip 2.4.0 release notes available from the following link.
ftp://ftp.triscend.com/fc240/release_note.htm

Click on "Known Issues", then "Soft Modules".