Here are 3 <div>s. The red bordered div contains the blue bordered div. And the blue bordered div contains the silver border div. Once the silver bordered div becomes absolutely positioned, its containing block is no longer the blue div but the initial containing block which is a rectangle with the dimensions of the viewport (see CSS 2.1, Section 10.1 on this). So, when the silver div becomes absolutely positioned, it should become exactly as wide as the red bordered div (Nota bene: this testcase removes padding and margin on the body element).

This div has style="width: 80%; border: solid red;"
This div has style="width: 80%; border: solid blue;"
This div has style="width: 80%; border: solid silver;"


The silver div position is now static.

When the silver div is absolutely positioned, it should be exactly as wide as the red div.

This bug has been reported by other reporters.