Done.
It seems working...
I mean, the Maxthon 5 detected the 4 and asked me if I wanted to import.
I did it with guest mode, so now I have a long list of all my accounts, and there's not a real page to edit.
I can edit and delete immediately, so I deleted a pair of "random" data that I invented when I was desperate.
Tomorrow I'll try better and let you know.
Now I'd like to discover the orgin of my issue. The only thing that I can see is that my MagicFill2.dat is updated everytime I use Maxthon (normal and portable)...or at least changes the date of modify (the access is always at Jan 2016)...I'll show you a screenshot.
By the way, thank you in advance to you all three...hope to not disturb you again...