Stylesheet border does not render correctly

Border (css border) does not render correctly under several circumstances:

Transparency: If the border color is RGBA, the border is rendered as a double border: internal half border is opaque, external has alpha.

Border-radius: the radius is rendered incorrectly:

• it seem like the border is rendered by adding several small lines for the radius, so when alpha color is applied, several layers are shown in the radius.
• When the border width is bigger than the border-radius, the border-radius disappear, with also some visual strange drawing.