Hello Hans!
If referencing to the same line, the line will be displayed twice. I tried Wolfgangs patch:
http://archive.contextgarden.net/message/20091018.091419.18877aa9.en.html
but it did not help.
\starttext
\startlinenumbering
\someline[a]We thrive in information--thick worlds because of our
marvelous and everyday ca-pacity to select, …\someline[b]
\stoplinenumbering
\inline[a] or \inline[b]
\stoptext
Greetings
Andreas