memory overrun/underrun assigning pointer

seems when i assign a pointer, im getting the last variable in one class overwritten. so i have the following code (note, nop's just for debugging purposes):

void OGLDevice::SetActiveWindow(Win32Window* wnd)
{
	__asm nop
	activeWindow = wnd;
	__asm nop
	ResetDevice(activeWindow->GetWidth(), activeWindow->GetHeight());
}

equates to this in assembly with vc2005 beta 2:

	__asm nop
00408073  nop              
	activeWindow = wnd;
00408074  mov         eax,dword ptr [this] 
00408077  mov         ecx,dword ptr [wnd] 
0040807A  mov         dword ptr [eax],ecx 
	__asm nop
0040807C  nop

now: this = 0x0012fcd5 wnd = 0x0012fcbc &(wnd->height) = 0x0012fcd4 obviously wnd->height is the last variable in my wnd class with the this class comming right after it. Seems when i do my pointer assignment, it writes data to both this->activeWindow (which is the first variable in the this class), and wnd->height. Both end up with an incorrect value how ever. If i take some variables out of my wnd class this does not occur. I assume this is due to memory alignment or padding?