[NTG-context] XeTeX "tex-text" mapping problem

Hi all, there seems to be a problem with the XeTeX engine and the "mapping:tex-text" feature for OpenType fonts. Try this: --- \usetypescriptfile[type-minion] \usetypescript[minion][uc] \setupbodyfont[minion,13pt] \starttext There is --- without any doubt --- a tiny problem. \stoptext --- together with the attached typescript file. Unfortunately, "---" is not replaced by an em dash :-( Substituting works flawlessly for plain XeTeX examples. Of course, replacing "---" with the proper Unicode em dash in the above source solves the problem (by avoiding it). Any hints as to what I've done wrong? Best, Oliver