There is an errata sheet for the 89c51rx2/01 (2nd gen) parts. Just pulling the PSEN line low would not start the bootloader. The workaround was to put capacitors on EA or PSEN to manipulate the power-up sequence.

I thought it was a cheezy solution.

Bob

I am going to try J.Guy's approach of setting ENBOOT and jumping to FC00.
For the moment though, I am using 89C51Rx2H parts that don't (apparently) have this problem.