This source extracted from the phobos unittests:

struct S1 
{ 
	cdouble val; 
}

void formatTest(S1 s, double re, double im)
{
	assert(s.val.re == re);
	assert(s.val.im == im);
}

unittest
{
	S1 s = S1(3+2.25i);
	formatTest(s, 3, 2.25);
}

void main() {}

compile with "dmd -unittest -m64 -O test.d" and run to see the assertions failing.
This does not happen with -m32 or without -O.

Here is the disassembly of the unittest code:

_D4test15__unittestL12_1FZv:
  0000000000000000: 55                 push        rbp
  0000000000000001: 48 8B EC           mov         rbp,rsp
  0000000000000004: 48 83 EC 10        sub         rsp,10h
  0000000000000008: 48 C7 45 F0 00 00  mov         qword ptr [rbp-10h],0
                    00 00
  0000000000000010: 48 C7 45 F8 00 00  mov         qword ptr [rbp-8],0
                    00 00
  0000000000000018: 4C 8D 45 F0        lea         r8,[rbp-10h]
  000000000000001C: F2 48 0F 10 0D 00  movsd       xmm1,mmword ptr [_TMP3]
                    00 00 00
  0000000000000025: F2 48 0F 10 05 00  movsd       xmm0,mmword ptr [_TMP4]
                    00 00 00
  000000000000002E: 48 83 EC 20        sub         rsp,20h
  0000000000000032: 66 48 0F 7E CA     movd        rdx,xmm1
  0000000000000037: 66 48 0F 7E C1     movd        rcx,xmm0
  000000000000003C: E8 00 00 00 00     call        _D4test10formatTestFS4test2S1ddZv
  0000000000000041: 48 83 C4 20        add         rsp,20h
  0000000000000045: 48 8D 65 00        lea         rsp,[rbp]
  0000000000000049: 5D                 pop         rbp
  000000000000004A: C3                 ret

The struct literal is initialized with two 0 values at offset 8/10.