I finally got it! After two days..

MOV R1,0
should be
MOV R1,#0!

I've copied those lines from a program
I am using for 10 months, and this is
the first time I've seen the error...

The reason it worked from FLIP is that BOOT ROM
has left R1 at a fixed state (ie. a value from
0 to FF, but always the same).

I haven't read anywhere, but I bet that the
memory 0-7F is undefined after power-up, right?

The time it took me to remove the programming cable
was enough for CPU to 'forget' the memory contents
below SFRs.

-------------------
The RES pin is still floating, and it works.

Does anyone have experience with ED2 regarding
brown-outs, etc? Should I implement a reset IC
or is internal circuit sufficient?

The ED2 should work up to 60MHz. I've programmed it
with FLIP (all 64k, several times) at 48MHz.

Does PSEN have internall pull-up?