CSSOM: getClientRects for table with caption

The CSSOM View Module describes how to get the client rects of a table at:
http://www.w3.org/TR/cssom-view/#the-getclientrects However, for tables with
a caption all but Firefox returns a single rect. Is there a reason why the
spec describes a different behavior than what 3 out 4 browsers use?

The following test case shows the issue:

http://www.plexode.com/cgi-bin/eval3.py#ht=%3Ctable%20id%3Dt%3E%0D%0A%20%20%3Ccaption%3EHi%3C%2Fcaption%3E%0D%0A%20%20%3Ctr%3E%3Ctd%3Eone%3Ctd%3Etwo%0D%0A%20%20%3Ctr%3E%3Ctd%3Ethree%3Ctd%3Efour%0D%0A%3C%2Ftable%3E&ohh=1&ohj=1&jt=document.getElementById('t').getClientRects().length&ojh=1&ojj=1&ms=100&oth=0&otj=0&cex=1

<http://www.plexode.com/cgi-bin/eval3.py#ht=%3Ctable%20id%3Dt%3E%0D%0A%20%20%3Ccaption%3EHi%3C%2Fcaption%3E%0D%0A%20%20%3Ctr%3E%3Ctd%3Eone%3Ctd%3Etwo%0D%0A%20%20%3Ctr%3E%3Ctd%3Ethree%3Ctd%3Efour%0D%0A%3C%2Ftable%3E&ohh=1&ohj=1&jt=document.getElementById('t').getClientRects().length&ojh=1&ojj=1&ms=100&oth=0&otj=0&cex=1>IE:
1
WebKit: 1
Opera: 1
Firefox: 2 -- erik