The following code:
-----
module evbug;
import std.stdio;

struct S {
  int last = 0;
  S opCall(int i) {
    writefln("%s %s", last, i);
    last = i;
    return *this;
  }
}

void main() {
  S t;
  t(1)(2);
  t(3);
}
-----
should output
=====
0 1
1 2
1 3
=====
(Note that opCall returns a copy of the original struct, so the first and last calls will be passed &t as 'this', but the second is passed a pointer to a copy)
With "dmd -run test.d", this all works fine.

However, when run with "dmd -inline -run test.d":
=====
0 1
1 2
2 3
=====
(note the last line)
The "return *this" seems suddenly to have compiled as a reference return instead of a value return. (This can be verified by making opCall print the address as well; the uninlined version will only report the same address for the first and last call, while the inlined version reports the same address every time)

GDC doesn't exhibit this problem, presumably because it uses the GCC inliner.