opacity of images over video

when placing a graphic with an irregular form created with a transparent channel (e.g. the colour white defined as transparent in a PNG file) over an interactive video on a slide the irregular form displays over the interactive video.because the white channel becomes transparent (when the opacity setting is set to 0) However, the same graphic place over interactive video by using the interactive video editor displays as a rectangular shape, because the transparent channel shows up as white. This is indesirable for creating interesting interacdtions. The same is true for Text items placed over interactive video. Why is this indiscrepancy there, and can it be fixed?