This setting gives an overfull hbox of exactly 3 points:
\setupitemgroup[itemize][each]
[joinedup,packed]
[symbol=n,distance=3pt,
align=right,itemalign=flushright,
stopper={.\,}
]
In the logfile: Overfull \hbox (3.0pt too wide) detected at line 7

Changing to distance=4pt makes the hbox 4pt too wide.
Changing to distance=0pt (or delete parameter) makes the hbox fit.

Why is this?
Apart from cluttering the logfile, I guess this hbox overflow signals something that can be bettered.

Hans van der Meer