Mohammad Hossein Bateni
22. August 2016 um 10:49
Same problem, item (6) of email below, observed with arabtype font.  See attached.  MWE follows.

\definefontfamily [myfamily] [serif] [arabictypesetting] [features=arabic]
\setupbodyfont    [myfamily]
\setupalign[r2l]
\setupdirections[bidi=global,method=two]

\setupmixedcolumns[register][direction=reverse]
When you have a font with large ascender/descender you can increase the linespacing (line key) or change the height/depth (height and depth keys) values for \strut.

\startsetups[register:interlinespace]
    \setupinterlinespace[height=0.6,depth=0.4,line=3.2ex]
\stopsetups

\setupmixedcolumns
  [index]
  [direction=reverse,
   setups=register:interlinespace]

Wolfgang