In one older post (very older) I reported the same problem (
http://phpbb.ulead.com.tw/EN/viewtopic.php?t=10067 ). I never figured out why it did no longer work. I am sure, that I had seen it also while overlapping images, which had of course no audio, but later it did not even work with videos having audio. But now with the SP there are good news: it works again

, but only for video, not for images

.
I sent this allready to Ulead. Hope they will fix it til the final release of the SP. I dont see any reason, why it should not work also without audio.
Okay, I know, there are many different other ways to see the duration, but none is so comfortable.