[NTG-context] displaylines in textetxt?

Is it impossible to typeset displaylines in textext called inside metapost? The gives an error: \starttext \startMPpage label(textext("$$\displaylines{a=b\cr}$$\strut"),origin); \stopMPpage \stoptext metapost/context/base/metafun.mpiv ! Missing } inserted. -- <inserted text> } <to be read again> \halign \displaylines ...spl@y \tabskip \zeroskip \halign {\hbox to \displaywidth {$… Though for example, \matrix,\cases seems to work. I already have put \unexpanded in front of the definition of \displaylines in math-pln.mkiv Hans van der Meer