Something must have been changed with buffers between the versions:
ConTeXt  ver: 2011.11.29 18:47 MKIV  fmt: 2011.12.31
and
ConTeXt  ver: 2012.01.09 10:08 MKIV  fmt: 2012.1.11

Formerly this was ok:
\startbuffer[abc]
whatever
\stopbuffer

Now I get: ! Missing } inserted.

Because running this in isolation goes without a problem, I suspect the change has to do with the project structure in which I use the buffer. But again, it worked in the past.

Hans van der Meer