[NTG-context] subformulas numbering doesn't work

Hi! The following example from http://wiki.contextgarden.net/Math/Display#Sub- Formula_Numbering doesn't work in MKIV: \startsubformulas[eq:1] \placeformula[eq:first] \startformula c^2 = a^2 + b^2 \stopformula \placeformula[eq:second] \startformula c^2 = a^2 + b^2 \stopformula \stopsubformulas Formula (\in[eq:1]) states the Pythagora's Theorem twice, once in (\in[eq:first]) and again in (\in[eq:second]). It produces formulas (1.a) and (2).