[web2py] Doubt with THEAD helper

[Skiros]

Hello !

I have a doubt using THEAD helper. THEAD("a", "b") gives me as result
"<thead>ab</thead>".
I expected "<thead><th>a</th><th>b</th></thead>".

Why is not the same operation like TR("a", "b")  = "<tr><td>a</
td><td>b</td></tr>" ?