[NTG-context] Strange t-bib behavior

Hello, I attach an example file which produces strange citation behavior: while the single citations ('\cite[authoryears][cordingley:90]' or '\cite[authoryears][walker:94]') work perfectly allright, the dual citation ('\cite[authoryears][cordingley:90,walker:94]') is being screwed up: (Cordingley et al., 1990, Walker, 1994 and , ) Any ideas where the problem lies? Thanks, Joh