Not the same issue, but I found that switching the independent book lock OFF allowed me to use the button by the rearview mirror and the key fob. I'd assumed ON was more logical, but then I don't know exactly what independent boot lock actually means. Seems like a poor Italian to English language conversion.
On my 147 all was fine. On my 147 GTA, the alarm went off every time I opened the boot without unlocking the car first.
Maybe try what Nev suggests, but I've not found any specific rhythm to Alfas and this!