In the latest beta (2018.08.10),
\defineregister[TesT]
\starttext
\startregister[TesT]{samples}
\input knuth
\page
\input ward
\stopregister[TesT]
\blank[3*big]
\placeregister[TesT]
\stoptext
produces on page 2 the index entry
samples 1
when one expects
samples 1–2
Alan