bug with glue and spaces in formulas?

[Otared Kavian <otared@wanadoo.fr>]

Hi Hans and all Contexters,

While discussing with David Munger about the Steps macros he wrote 
for presentations in ConTeXt (see the thread \presentationstep), we 
noticed that there seems to be a problem with "white spaces" or glue 
around some "binary operators" such as +, - and =.
Please see the result of the following sample.

Best regards: OK

%%%% begin file test-glue.tex
\starttext
This is to verify how the space, or glue, is controlled in \ConTeXt.

First some binary operators ``$\in$'', ``$+$'', ``$-$'' and ``$=$'' 
without grouping braces:
\placeformula[eq:plain]
\startformula
x\in \Omega \subset {\Bbb R}^N,\quad\quad -\Delta u + u -u^3 = f.
\stopformula
Next the same with braces
\placeformula[eq:braces1]
\startformula
x{\in} \Omega {\subset} {\Bbb R}^N,\quad\quad {-}\Delta u {+} u {-u^3} {=} f.
\stopformula
Note how the spaces around the signs $\in$, $+$, $-$ and $=$ have 
shrinked. The problem seems to appear when these are actually binary 
operators (that is $+1$ and ${+}1$ give the same result, while 
$1+2=3$ is different from $1{+}2{=}3$).

I haven't tried all such binary operators, but it seems that this 
happens with all of them: compare $A \cap B$ and $A{\cap}B$, or 
$A\cup B$ and $A{\cup}B$.

\stoptext
%%%%% end file test-glue.tex