To explain why the two differ (where the second is just an unwrapped loop, pretty much otherwise equivalent to the first):

Each flipflop operator has its own independent hidden state variable in the pad. It acts like a my $flipflopstate at the top of the enclosing sub or file, only a different variable for each flipflop in the sub/file.

Thus, in your second example, the first 1..10 gets set true (because $. is 1) but none of the later ones are (because they never pass the beginning check for $.==1).

In the first example, the flipflop returns true 10 times because it meets the $.==1 check the first time and doesn't meet the $.==10 check until the 10th time.

Note that because the hidden state acts like sub-scoped lexical, a recursive call to the sub will start with a fresh state, and ditto multiple threads in the same sub.