Problem with horizontal dock panel when background is transparent

Manjaro xfce dock panel not refreshing when horizontal and the background is transparent. I tried to find why is this happening but it doesn’t make sense.

When in vertical it works just fine the background is transparent and the apps change but when it is horizontal, if i make a change the old frame stays in the back.

I also tried to put as background a transparent black color with 0.1 opacity but the 0.1 adds up and after a while the color of the background is black again. I saw similar issue before a month so i thought i should make another issue about it

is this a bug? help me if you can because i think the semi-transparent panel is very cool.