Hi Hans,

this got posted on the DANTE list today.

  \definefontfeature [quite_wide] [extend=1.5]
  \definefont [mainfont] [file:Iwona-Regular.otf]
  \definefont [widefont] [file:Iwona-Regular.otf*quite_wide]

  \starttext
    \mainfont
    {\widefont foo} %% comment this line and “bar” is fine
    bar
    {\widefont baz}
  \stoptext

The example defines two fonts with the same base font. If the
scaled variant is used before the regular one then the latter
will appear scaled as well and the spacing (bboxes?) gets messed
up.

I suspect a relation to this old issue:

  http://tracker.luatex.org/view.php?id=829

but if I substitute “slant” for “extend” the behavior is
different.

Best,
Philipp