This used to work in earlier versions of MKIV, but does no longer—the page sets without complaint but the footer does not appear.

A minimal example:

\definehead[BookTitle][title]
\setuphead[BookTitle][header=high,footer=BookTitlePage]
\definetext[BookTitlePage][footer]
[\vbox{\tfx
\centerline{Some text}\par
}
]


\starttext
\BookTitle{Title}
\input knuth\footnote{\input ward}
\stoptext

Is there a problem with \definetext?

Alan