[metapost] boxit and grouping

[Ovidiu Gheorghies]

Hi.

I try to compile the code

  boxjoin(a.se=b.nw; a.ne=b.nw);
  boxit.aaa(btex A etex);
  boxit.bbb(btex B etex);
  aaa.nw = (30,30);
  drawboxed(aaa, bbb);
  
   begingroup
     save aaa, bbb, a, b;
     boxjoin(a.se=b.nw; a.ne=b.nw);
     boxit.aaa(btex A etex); % line 71
     boxit.bbb(btex B etex);
     aaa.nw = (50,50);
     drawboxed(aaa, bbb);
   endgroup;

but I get the error

! Redundant or inconsistent equation.
<to be read again>
                   ;
beginbox_->...:=(EXPR1);pic_(SUFFIX2)=nullpicture;
                                                  
for._p_=(TEXT3):pic_(SUFFI...

boxit->..."boxpath_","sizebox_",(SUFFIX2),(TEXT3))
                                                  
;generic_declare(pair)_n.s...
l.71      boxit.aaa(btex A etex)
                                ; % line 71

I ran into this problem while working on a library: the code 
generated by my macros can be reduced to something similar.

Thanks in advance for any ideas,
Ovidiu Gheorghies