Some of them allowed to use MID$ for the left-hand side of an assignment to replace a substring, which is also unexpected.
A$ = "ABCD"
MID(A$,2,2)="12"
PRINT $A
>A123
x = [1,2,5,6]
x[2:2] = [3,4]
print(x)
(Slice notation can be used on any collection, not just lists, but you can't use it in assignment like that for strings because they're immutable, so you'd have to convert to a list of characters and back.)