\startbuffer[ABC]%
{} Braces at beginning fails with buffer
\stopbuffer
\starttext
\getbuffer[ABC]
\stoptext

Error message:
! File ended while scanning use of \dododowithbuffer.
<inserted text>
                 \par

Remove the {}'s at the beginning and all is well.
The culprit however is the % in the first line; remove and the braces  
do no harm.
I suspect that a missed newline is the cause. If that cannot be  
remedied, I advise adding a warning in the manual.

Hans van der Meer