Subchart inconsistency when using chart.flow function

[jvorcak]

C3 version: 0.4.10
D3 version: 3.5.6
Browser: Firefox 57.0.4
OS: OS X

https://codepen.io/anon/pen/jYexmM

Hi,

First of all thank you for this awesome library.
I tried to prototype one of the graphs I need to create and I run into an issue that my subchart looks inconsistent with the rest of the graph after data is added with chart.flow function. Also there is quite disturbing animation, but I'm mostly worried about an inconsistency.

Thanks for having a look and please let me know if I can be of any help.