contextLimitedVector gives missleading warning when entering in incorrect answer.

[somiaj]

When using contextLimitedVector.pl with a Formula, negative signs get a warning that they are not allowed in this context when the answer is incorrect (but correct answers are accepted). Example problem:

DOCUMENT();      
loadMacros(
    'PGstandard.pl',
    'PGML.pl',
    'contextLimitedVector.pl',
);
Context('LimitedVector')->variables->are(t => 'Real');
Context()->flags->set(ijk => 1);
$v = Formula("<-11t^2,4t,-4t^3>");

BEGIN_PGML
    [`[$v]=`] [_]{$v}
END_PGML
ENDDOCUMENT();

If an incorrect answer is entered, such as -t^2i+4tj-4t^3k, the warning "In this context, '-' can only be used with Numbers or i,j and k" is given. It still accepts correct answers.