There seems something very much amiss with \halign in later ConTeXt versions.

This typesets fine in PlainTeX and is an example taken from a textbook.

  \tabskip=1em\halign{%

  \hfil\it#\hfil&\hfil#\hfil&#&\hfil#\crA&B&C&D\cr}

Also in contextversion 2012.05.30 (from a TeXlive distribution).

But it fails at least in ConTeXt  ver: 2013.03.20 10:34 MKIV

and in ConTeXt  ver: 2013.04.16 12:08 MKIV beta

with the following error

! Only one # is allowed per tab.

system          > tex > error on line 5 in file fixedwidth.tex: Only one # is allowed per tab ...

 1     \starttext

 2     contextversion=\contextversion\par

 3     \tabskip=1em

 4     \halign{%

 5 >>  \hfil\it#\hfil&\hfil#\hfil&#&\hfil#\cr

 6     A&B&C&D\cr}

 7     \stoptext

l.5 \hfil\it#\hfil&\hfil#

                       \hfil&#&\hfil#\cr

Why? How primitive it may be, I would like to use \halign now and then.