according to the SCSS reference in http://sass-lang.com/docs/yardoc/file.SASS_REFERENCE.html#division_and_slash that is precisely what is expected. try putting it into a mixin:
@mixin fontandline{
font: 14px/12px;
}
then, whenever you need to use it again, just write it like that:
@include fontandline;
see http://sass-lang.com/docs/yardoc/file.SASS_REFERENCE.html#mixins for more information.
EDIT:
according to latest documentation (see link above) the following code
p {
$font-size: 12px;
$line-height: 30px;
font: #{$font-size}/#{$line-height};
}
should be compiled to
p {
font: 12px/30px;
}