% Initially, re-height of the current row and setting
% \cals@last@row@height was in '\cals@issue@row'.
% After implementing row spanning, this actions were moved
% to \erow. Unfortunately, I forget to move the second action.
\begin{calstable}
\cals@setpadding{}
\cals@setcellprevdepth{}
\colwidths{{100pt}{100pt}{100pt}}

\thead{%
\brow
 \cell{h1}\cell{h2}\cell{h3}
\erow
}

\brow
 \cell{a1}
 \cell{a2}
 \cell{a3}
 \ht\cals@current@row=30pt
\erow
\showthe\cals@last@row@height

\brow
 \cell{b1}
 \nullcell{ltr}
 \nullcell{ltr}
 \ht\cals@current@row=40pt
\erow
\showthe\cals@last@row@height

\brow
 \cell{c1}
 \nullcell{lbr}\spancontent{s2}
 \nullcell{lbr}\spancontent{s3}
 \ht\cals@current@row=50pt
\erow
\showthe\cals@last@row@height

\end{calstable}