I have the following code that does simple type checking:

void check(T)(T t)
{
    writefln(T.mangleof);
    writefln(typeof(t).mangleof);
        
    writefln(T.sizeof);
    writefln(typeof(t).sizeof);

    writefln(T.stringof);
    writefln(typeof(t).stringof);
}

It should output the same information twice, since is(typeof(t) == T) is true.
Let's run tests:

Test one:
check(42);

Output:
i
i
4
4
int
int

Test two:
check(0.0);

Output:
d
d
8
8
double
double

Ok so far. Test three:
check(42);
check(0.0);
Output:
i
i
4
4
int
int
d
i
8
4
double
int

Whoops! Results got mixed. Looks like typeof(t) returns wrong result now!