problem with transparency

I have a gif picture for which one color will be use as transparency.

In phAB, if I include my picture in a ptLabel I can choose my transparency
color, that works fine.

If I include my picture in a ptImageArea, I can also choose my
transparency color, preview works fine, but out of the image editor,
there’s no more transparency !?

In fact I didn’t find any doc about PtImageArea. What is it?