Padding-right is not rendered in an overflowed block-level element

UPDATE: according to CSS expert and guru, Alan Gresley, the CSS 2.1 spec does not cover precisely how this testcase should be rendered. So, I am removing this testcase for now... I need to better understand the spec, in particular, the consequences of CSS 2.1, section 10.3.3 Block-level, non-replaced elements in normal flow which states:
"If all of the above have a computed value other than 'auto', the values are said to be 'over-constrained' and one of the used values will have to be different from its computed value."

Steps to reproduce: scroll horizontally the thick bordered box to the right, as far to the right as possible

Expected results: There should be a 50px gap on the right hand side of the green block (a padding-right of 50px should be rendered)

Actual results in Internet Explorer 8 beta 1: there is no gap (padding-right is 0)

Actual results in Safari 3.1: there is no gap (padding-right is 0); Bug 13632: Overflow scrolling doesn't account for bottom padding (and padding-right)

Actual results in Opera 9 beta 1 build 8031: there is a gap of 111px (padding-right is 111px); this is bug 186876

Actual results in Firefox 2.0.0.13: there is no gap (padding-right is 0); this is bug 47710: Overflowed content does not take into account inner padding

Note: Internet Explorer 6 and Internet Explorer 7 render this testcase accordingly.

Reference: there is nothing in CSS 2.1, section 10.3.3 Block-level, non-replaced elements in normal flow stating that padding-right should not be rendered.