Branch is incorrectly recognized as master in CircleCI

Description

While my git branch is not master and codecov-node client seems to detect it correctly, codecove site displays it as master.

Repository

Branch is detected correctly by codecov client:

==> Configuration: 
    Endpoint: https://codecov.io
{
  commit: 'e4bf7d18b5571a059cb81fba59702fd42e3b6e9e',
  branch: 'codecov-config',
  package: 'node-v3.5.0'
}

Steps to Reproduce

Expected behavior:

Shown as master branch: https://codecov.io/gh/teppeis/duck/commit/e4bf7d18b5571a059cb81fba59702fd42e3b6e9e

Actual behavior:

Shown as codecov-config branch.

Flakiness?

Everytime: ttps://codecov.io/gh/teppeis/duck/commits

Versions

Mac Chrome 75