Nested templating variable precedence

Hi,

Considering a template like
```
# generic.yaml
!Defaults
name: Unknown name
greeting: Unknown greeting
---
phrase: !Format "{greeting} {name}"
```

Which is templated once, with results as expected (`phrase: Hello Mark`):

```
# hello_mark.yaml
!With
template: generic.yaml
vars:
name: Mark
greeting: Hello
```

and then another template on top of the previous one

```
# hello_john.yaml
!With
template: hello_mark.yaml
vars:
name: John
```

I expected it to result in `phrase: Hello John` but rather I got still `phrase: Hello Mark`. So it seems that the first (lower level) variables within the !With tag cannot be overriden by higher level !With templates.

Is this by design? Thanks!