I think the MCC is not supposed to deal with 9 bit UART communication at all.
I think it is not a bug, I think it is a deliberate simplification, or omission.
There are many features of PIC hardware, that is not supported by MCC code.
Especially for PIC32MX devices.
In PIC32MX devices, the UART peripheral may be set up to generate parity bits in the 9. bit in hardware.
For a communication protocol using 9 bit communication, you should modify the generated code as needed.
MDB ? are you dealing with Microchip command line DeBugger, or something else?