Using both parent_profile and source_profile in the same profile does not work

[jheino]

After version 5.3.0, using both parent_profile and source_profile in the same profile does not work. My use case is to set mfa_serial in the parent profile and then import that to other profiles without setting mfa_serial everywhere. I understand that the change in 5.3.0 was made to prevent a profile from referring to itself but it seems it might have this side effect.

My ~/.aws/config:

[default]

[profile root]
mfa_serial=arn:aws:iam::123456789012:mfa/User

[profile dev]
region=eu-west-1
role_arn=arn:aws:iam::987654321098:role/Developer
parent_profile=root
source_profile=root

aws-vault exec --debug dev:

2020/02/18 09:19:45 aws-vault v5.3.1
2020/02/18 09:19:45 [keyring] Considering backends: [file]
2020/02/18 09:19:45 Loading config file /home/jukka/.aws/config
2020/02/18 09:19:45 Parsing config file /home/jukka/.aws/config
2020/02/18 09:19:45 [keyring] Expanded file dir to /home/jukka/.awsvault/keys/
aws-vault: error: exec: Error getting temporary credentials: profile dev: credentials missing

If I replace parent_profile with mfa_serial it works as usual.