[NTG-context] ## not permitted in the presence of &.

Hi, I run into trouble with mkiv (ConTeXt ver: 2012.05.30 11:26 MKIV fmt: 2012.7.7 int: english/english). A small example: \starttext \def\c#1#2{\halign{##\hfil&##\cr\bf#1&\quad#2\cr}} \c{11}{this} \stoptext gives and error: ! Only one # is allowed per tab. This runs error-free under mkii (pdftex, xetex), plain tex (luatex, xetex), latex (luatex) etc. Would someone comment? Thank you, Eythan