It appears that descriptions generate a spurious
Missing character: There is no ^@ (U+0000) in font lmroman12-regular!
log message. MWE:
\definedescription[oops][]
\starttext
\oops{Where}is the U+0000?
\stoptext
The messages appears in the log once for each description in the document.

This happens with the current (2014-04-15) beta. It does not happen with TL13.

--
Rik Kabel