Chart lines representing separate *tables* are linked in the special case where two grouping tags are reversed

[gefaila]

Steps to reproduce:

You will need:

1. Data which undergoes first a pivot() operation to make into columns, and then a group() operation whereby it's grouped by two of those columns e.g.
   |> pivot(rowKey:["_time"], columnKey: ["_field"], valueColumn: "_value")
|> group(columns: ["_cycle","_step"], mode:"by")
2. When viewing the raw output this apparently works correctly. There are separate tables (in my case 117), one for each unique combination of "_cycle" and "_step"
   
3. This yields the following data
   2020-12-17-09-49_chronograf_data.xlsx
4. The issue comes when charting the output

Expected behavior:
When charting the output I expect that lines representing each separate table of data are:

• unconnected (i.e. there is no line connected data from different tables)
• unique in colour
  I also expect to have the same number of lines as I have tables. One line for each table

Actual behavior:
What you actually get is

• a separate colour for each _cycle but not for each ["_cycle","_step"] combination that the tables represent
• line joins between certain tables. Interestingly there are only joins between lines for tables where they have reversed tags. So the line for table '#'31 (_cycle 32, _step 36) is joined to the line for table '#'97 (_cycle 36, _step 32)
  
• this joining of similar tables means that there are significantly less lines than tables

Environment info:
InfluxDB version: InfluxDB Cloud 2.0

[gefaila]

A workaround to the bug is
|> map(fn: (r) => ({ r with _cycle_step: float(v: r._cycle) + float(v: r._step) /100.0 }))
|> group(columns: ["_cycle_step"], mode:"by")

This produces exactly the same 117 unique tables
But for some reason the Chart line now has no problem drawing these with the expected separate lines for these identical tables.

[gefaila]

Therefore it's the charting function which appears to be at fault

[gefaila]

@danxmoran and @russorat
This has been open for a while.
Any fix proposed/implemented?