It seems the problem was caused by older user-base files repeairing some problems I had with older versions. 

I find the following problems:

(1) \starthiding-\stophiding is not functioning. Minimal example:

\starttext

\starthiding

CRY: 

\stophiding

Hello world.

\stoptext

Error message: ! Too many }'s.

\buff_stop #1->\egroup 

                       \getvalue {#1}

l.7 \stophiding