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