[NTG-context] Persian digits in math formulas

Dear All, Hello, I am trying to use Persian digits in math formulas. My document reads: \font\4 = {name:dejavusans} at 10pt \font\5 = {name:dejavusans} at 7pt \font\6 = {name:dejavusans} at 5pt \textfont4=\4 \scriptfont4=\5 \scriptscriptfont4=\6 \Umathcode`3="1"4`۳ \definefontfeature [persian] [arabic] \mainlanguage[pe] \starttext \definedfont[dejavusans*persian] \setupalign[r2l] این یک آزمایش است. 3+2=5 $3+2=5$ \setupalign[l2r] This is a test. 3+2=5 $3+2=5$ \stoptext However in the output the replaced digit "3" disappears. Any help is gratefully appreciated. Thanks, Mingranina