I got another European adapter, just like the one you described but the problem remains.
I checked and I can’t measure any resistance between LED10 and any of the other LEDX connections. I double-checked continuity between LED10 and the other LEDX connections and also got nothing, so no short circuit.
I also checked for shorts betweeen pin 15 on the ATMega chip and the other pins and also no problems.
I used my arduino to light up D45 and when I do this D410 and D105 also light up (although only slightly, probably as I’m only using the 3.3V output).
When D45 is ON, 4 is HIGH and 5 is LOW. So I don’t understand how D410 and D105 can both be on simultaneously. For D410 to be on, 4 is HIGH and 10 is LOW. But for D105 to be on, 10 needs to be HIGH and 5 is LOW. So how can 10 be both high and low simulataneously to create this situation? The same goes of course for the other leds which come on along side D16 and D42.
I’d be very grateful for your input again.