[NTG-context] ConTeXt, XeTeX for Linux and xdvipdfmx

Hi, It seems that some things doesn't work well with ConTeXt and XeTeX for Linux. For example image inclusion (jpg, png, pdf) with \externalfigure or \useexternalfigure doesn't work, but does with xdvipdfmx \special's (\special{pdf: image ...}). Also, \setuppapersize doesn't work (e. g. \setuppapersize[A5][A5] does the same as \setuppapersize[A5][A4], being A4 the default). But \color seems to work well. Are these ConTeXt bugs (related to \special's) or Linux XeTeX-xdvipdfmx bugs? Thanks in advance, Ricard