I'm not able to reproduce this issue. In a node console I can run:

> var p = mustache.parse('{{#personLink}}{{#person}}{{name}}{{/person}}{{/personLink}}')
undefined
> JSON.stringify(p)
'[["#","personLink",0,15,[["#","person",15,26,[["name","name",26,34]]]]]]'

Please provide more information about how you're calling the function.

Here is the bug
Mustache.to_html(
'{{#personLink}}{{#person}}{{name}}{{/person}}{{/personLink}} ',
{
personLink:function(){
return function(text,render){
return "a"+render(text)+"/a";
};
},
person : {name : 'me'}
}
);
it causes Error: Unclosed section: 'person' {{#person}}{{name}}
If I use '{{#personLink}} {{#person}}{{name}}{{/person}} {{/personLink}} '
I have the expected result a me /a (with spaces)

Thanks for this bug report. It was a subtle bug! This is fixed in version 0.7.2.