oops, seems I made my answer very quick and forgot some important thing... Sorry.
1) Could you post your code, please?
2) What whould I do:
+ set UART to 9 bits mode with RB8 set to "1";
+ use modern C51 with FE bit;
+ set correct bit rate;
+ make simple UART ISR (see above).

Now how does it look.
- UART detects start bit;
- it receives 7 data bits and parity bit as 8th one into SBUF;
- it receives 9th bit which is first stop bit: if it is not "1" then reception will be drop;
- Frame Error feature detects second stop bit: if it is not "1" then it sets FE bit to indicate that stop bit (in our case it is SECOND stop bit) is invalid;
- ISR is executed and so:
a) check for FE bit: if it is set then ignore received byte and clear FE as well;
b) load SBUF into ACC and then look at P flag of PSW. At this point I should recommend you to do real tests because I never sure about what does mean Even/Odd parity: some vendors say that is set, another - reseted. Just test it. If wrong condition is detected then ignore received byte.

Regards,
Oleg