When HTML 4 rules attribute is defined for rows, cols or groups, then the border-collapse value must be collapse according to CSS 2.1.

Update January 12th 2009: This bug is INVALID.
From the beginning, I wrongly assumed that currentStyle (and then, later, runtimeStyle) equated/was for IE the W3C equivalent of getComputedStyle. My mistake. Note that I would never have filed this bug if IE had supported DOM 2 CSS getComputedStyle() in the first place.

Table with rules="cols"
THead Row0 Cell0	THead Row0 Cell1	THead Row0 Cell2	THead Row0 Cell3	THead Row0 Cell4
THead Row1 Cell0	THead Row1 Cell1	THead Row1 Cell2	THead Row1 Cell3	THead Row1 Cell4
TFoot Row0 Cell0	TFoot Row0 Cell1	TFoot Row0 Cell2	TFoot Row0 Cell3	TFoot Row0 Cell4
TBody Row0 Cell0	TBody Row0 Cell1	TBody Row0 Cell2	TBody Row0 Cell3	TBody Row0 Cell4
TBody Row1 Cell0	TBody Row1 Cell1	TBody Row1 Cell2	TBody Row1 Cell3	TBody Row1 Cell4

Table with rules="rows"
THead Row0 Cell0	THead Row0 Cell1	THead Row0 Cell2	THead Row0 Cell3	THead Row0 Cell4
THead Row1 Cell0	THead Row1 Cell1	THead Row1 Cell2	THead Row1 Cell3	THead Row1 Cell4
TFoot Row0 Cell0	TFoot Row0 Cell1	TFoot Row0 Cell2	TFoot Row0 Cell3	TFoot Row0 Cell4
TBody Row0 Cell0	TBody Row0 Cell1	TBody Row0 Cell2	TBody Row0 Cell3	TBody Row0 Cell4
TBody Row1 Cell0	TBody Row1 Cell1	TBody Row1 Cell2	TBody Row1 Cell3	TBody Row1 Cell4

Table with rules="groups"
THead Row0 Cell0	THead Row0 Cell1	THead Row0 Cell2	THead Row0 Cell3	THead Row0 Cell4
THead Row1 Cell0	THead Row1 Cell1	THead Row1 Cell2	THead Row1 Cell3	THead Row1 Cell4
TFoot Row0 Cell0	TFoot Row0 Cell1	TFoot Row0 Cell2	TFoot Row0 Cell3	TFoot Row0 Cell4
TBody Row0 Cell0	TBody Row0 Cell1	TBody Row0 Cell2	TBody Row0 Cell3	TBody Row0 Cell4
TBody Row1 Cell0	TBody Row1 Cell1	TBody Row1 Cell2	TBody Row1 Cell3	TBody Row1 Cell4

Expected results: Section 17.6.1 of CSS 2.1 says "In this model [border-collapse: separate model], (...) Rows, columns, row groups, and column groups cannot have borders (i.e., user agents must ignore the border properties for those elements)."

Section 17.6.2 of CSS 2.1 says "In the collapsing border model, it is possible to specify borders that surround all or part of a cell, row, row group, column, and column group. Borders for HTML's 'rule[s]' attribute can be specified this way."

Firefox 2.x, Firefox 3, Opera 9.x, Safari 3.0.4, Konqueror 3.5.8, NS 7.2, Seamonkey 1.x, Seamonkey 2.x, K-meleon 1.x, Galeon 2, Epiphany 2 all pass these 3 tests.

This bug has been reported at connect's IE beta feedback as bug 351855.

Update January 12th 2009: This bug should be (otherwise has been) closed by IE Team since runtimeStyle object does not return the computed value of a property like the W3C DOM 2 CSS getComputedStyle