can anyone familiar with the matter explain the reason for this change?

    == 1.1 Earmuffed Vars Are No Longer Automatically Considered Dynamic. ==

    (def *fred*)
    => Warning: *fred* not declared dynamic and thus is not dynamically rebindable, but its name suggests otherwise. Please either indicate ^:dynamic ** or change the name.

I generally agree with the old Bertrand Meyer's advice that if you have a "you should never do X" in a language's documentation then the language should just not permit it, so this strikes me as strange.