[NTG-context] setuplabeltext doesn't adjust the part label (with MkIV)

setuplabeltext doesn't seem to adjust the part label. Here's a minimal example: \setuphead[part][placehead=yes] \setuplabeltext[part=Part~] \starttext \part{pt} This is a part. \stoptext With MkIV (e.g. on live.contextgarden.net), the part heading is just "1 pt". With MkII, it is "Part 1 pt" as expected. (setuplabeltxt does work for chapter labels, with either context version.) -Sanjoy