[NTG-context] Fonts inside eqno{}

Hello all! I'm interested in change the natural numbering of one equation with \eqno{} but it does not follow the main font selected. A minimal example: %%%%%%%%%%%%%%%%%%%%%% \usemodule[simplefonts] \setmainfont[Linux Biolinum O] \setmathfont[Linux Biolinum O] \starttext I have the following expression \placeformula \startformula y = Z \beta_1 + Y \beta_2 + u \stopformula that changes to % \placeformula \startformula y = Z \beta_1 + Y \beta_2 + W_1\tau + u \eqno{ (1')} \stopformula \stoptext ​%%%%%%%%%%%%%%%%%%%%%%​ ​I would like the (1') ​keep the same kind of font than (1). Any hint will be appreciated. Thanks! -- «...my role is to be on the bottom of things.» Donald Knuth