Visual Studio's Python type inference seems to be going crazy?

Question

I have the following code, and its type is (not) being inferred in a very bizarre fashion.

What's confusing is that this is not just a typical failure of the engine to infer types, but rather it's exhibiting such strange behavior that I cannot even understand where or what the bug might be.

Can someone explain what is going on? Why do the order and the presence of the statements that assign to x, y, and z affect the types of each other?

(For your convenience, I've added a suffix indicating the inferred type, so z1__int is inferred as int.)

def lmap1(func, items):
    return [func(item1) for item1 in items]

def tmap(f, items):
    return tuple(lmap1(f, items))

def a():
    f = lambda i: i
    items = [1]
    x1__unknown = tmap(f, items)[0]
    y1__unknown = tuple(lmap1(f, items))[0]
    z1__int     = tuple([f(item1) for item1 in items])[0]

def b():
    f = lambda i: i
    items = [1]
    y2__int     = tuple(lmap1(f, items))[0]
    x2__unknown = tmap(f, items)[0]
    z2__int     = tuple([f(item1) for item1 in items])[0]

def c():
    f = lambda i: i
    items       = [1]
    y3__unknown = tuple(lmap1(f, items))[0]
    x1__unknown = tmap(f, items)[0]