Are you saying that the IE0 interrupt will not interrupt the RI or TI interrupt, in the middle of servicing the RI or TI interrupt
No it will not, interrupts of the same IP priority do not interrupt each other.

IE0, IE1, TF0, TF1 and they all interrupt the serial interrupt routine ? Assume each interrupt routine is 100 usec long
Which is a way too high an execution time for interrupts. As I stated, my statement was valid only for good designs with decent ISRs.

Erik