source_profile only sources credentials?

Took me a while to realise I had to explicitly set the `region` for each profile despite using `source_profile` to base the new profile on an existing one that defined a `region`, given that `source_credentials` also exists, is it intended behaviour for `source_profile` to not actually source a profile?

```
$ cat .aws/config
[default]
region = us-east-1

[profile solutions]
role_arn = arn:aws:iam::xxxxxxxxxxxxxx:role/solutions
source_profile = default
$ aws ec2 describe-availability-zones
{ ... snip ... }
$ aws ec2 describe-availability-zones --profile solutions
You must specify a region. You can also configure your region by running "aws configure".
```