Multi y-axes and seriesName causes exception

[FG-Samuli]

Line and bar charts. I faced this on my own application, but tried it in the codepen editor too.
Reproduce steps:

• -create several named series
• -create at least 2 yaxis
• -give same name to last series and to another yaxis seriesName

var options = { chart: { type: 'line', }, series: [{name: "First", data: [1,3,5,7,9]}, {name: "second", data: [1, 2, 3, 4, 5]}, {name: "foo", data: [11, 12, 13, 14, 15]} ], yaxis: [{ seriesName: "First", title: { text: "First" }, }, { seriesName: "this causes problems", title: { text: "Problem" }, }, ] }
Above works but
if I change the second y-axis seriesName from "this causes problems" to "foo", rendering fails.

Why? Is this bug or do I understand something wrong.

[FG-Samuli]

I found the problem. There are different amount of series than yaxis