Re: SetLayeredWindowAttributes()?

The docs say: "once SetLayeredWindowAttributes has been called for a
layered window, subsequent UpdateLayeredWindow calls will fail until
the layering style bit is cleared and set again".

That seems pretty straightforward, but I find that I can freely make
a layered window (text with alpha, transparent background) "blink"
with code like that below and without explicitly touching the
layering style bit.

case WM_TIMER :
if ( wParam == FLASH_TIMER )
{
if ( pOSD->bToggle )
SetLayeredWindowAttributes(hWnd, CR_BACK, 0,
LWA_COLORKEY | LWA_ALPHA);
else
SetLayeredWindowAttributes(hWnd, CR_BACK, pOSD->alpha,
LWA_COLORKEY | LWA_ALPHA);
pOSD->bToggle = !pOSD->bToggle;
}

Though I haven't checked the return value,
SetLayeredWindowAttributes() does not seem to be failing.