Perl doesn't see things as left-to-right as you do.

"scalar" in "scalar ( (1,2) x 5 )" acts on "x", not "(1,2)".
The return value of "()x" in scalar context is (join '', map LHS, 1..RHS).

Similarly, "scalar" in "scalar ( ($a) = 5 )" acts on "=", not "($a)".
The return value of "()=" in scalar context is the number of items returned by its RHS.

Not a bug. In both case, the code works as designed and as intended.