I've just recalled a quirk with v1.0.2f.
Before loading a new sysex and after a factory reset, you need to go into the FCB and manually set "Sysex Rcv".
Boot while holding the DOWN pedal. when the boot process finishes, the GLOBAL CONFIGURATION>DIRECT SELECT LED will be lit.
Press the UP pedal twice (thrice? I forget). The GLOBAL CONFIGURATION>CONFIG LED will be lit.
Press the "7" pedal. The LED will light. Press and hold the DOWN pedal until the reboot process starts.
The FCB should now be in RECEIVE SYSEX mode.
This process changed with later versions of UNO, and is unnecessary with UNO2, so I just forgot about it until now.