Variable existence in extended layout depends on block usage

Following example raises notice about undefined variable `$var`:

``` latte
// view.latte
{extends './layout.latte'}
{var $var = 'ok'}


// layout.latte
{$var} // undefined variable
```

but this works:

``` latte
// view.latte
{extends './layout.latte'}
{var $var = 'ok'}
{block #test}


// layout.latte
{$var}
{include #test}
```

This is very confusing behaviour. Is it possible to fix it?
