I put a thinrule in a table as follows:

\starttext
\bTABLE
\bTR\bTD\thinrule\eTD\eTR
\eTABLE
\stoptext

It worked fine under MKII. However, when I switched to MKIV (both current and beta) I got the following error message:

! Missing { inserted.
<inserted text>
{
<to be read again>
&
<inserted text> ...blrow \makeTBL 1 1 \nexttblcol
\endtblrow
\flushtbltoks ->\begintbl \the \tbltoks
\endtbl
\endTBL ...x {\trialtypesettingtrue \flushtbltoks
}\lettbldis \maximumcol \z...
\eTABLE ...}}\eTBL }\removeunwantedspaces \endTBL
\stopTBLprocessing \fi \eg...
l.4 \eTABLE

Is this a bug?
Is there a workaround?

Thanks,
Bart