Series bar stops stacking after no entry for that series

C3 version: 0.6.14 (also happens with 0.7)
D3 version: v5
Browser: Chrome 74
OS: MacOS

https://jsfiddle.net/dayvidwhy/prq1z0wd/1/

Red series 'o7' stops stacking after there is no value for that date.

If you put in a value for that date it goes back to stacking as intended for the last bar.

https://jsfiddle.net/dayvidwhy/hsp0yx67/1/

Is this the intended behaviour?

Start by running the two linked JSFiddle reproductions in Chrome and compare the series data for the missing date. Trace the stacked-bar rendering path from the reproduction to identify why series 'o7' stops stacking, then confirm that both datasets produce the intended stacking behavior.

Written by the indexing model from the issue text.