rowspan differences between IE8/Firefox and Safari/Opera

Attached is an html example that uses rowspan.
 
Opera and Safari don't seem to render as expected. Firefox and IE8 do.
 
Safari and Opera need a rowspan of 2 or they're not happy while a rowspan of 3 works fine in Firefox and IE8.
 
Do Firefox and IE8 have the *correct* rendering, or at least the rendering the makes the most sense given the markup?

I see:
<http://www.whatwg.org/specs/web-apps/current-work/multipage/tabular-data.html#attr-tdth-rowspan>
<http://www.whatwg.org/specs/web-apps/current-work/multipage/tabular-data.html#table-model>

, but not sure.
 
Thanks

-- 
Michael