Line plot does not show all data if there are duplicate x-values

Problem/Motivation

This might be a feature request instead of a bug report. What I'm wanting is to create a time-series plot with connected points. It's cumulative, so if there are multiple points with the same x-value, they should all be plotted (with different y-values). I'm using your View Cumulative Field module to get the y-values :)

If this is a feature request, it's that I'd like to be able to connect the points in a scatterplot.

Looks like for Plotly, though, line plots are just connected scatterplots, so a line plot should do what I want. And it mostly does (see below plot).

Side note: this behavior is different than a few of the other plotting backends I tried with Charts - most of them treated the dates as a category and not a true x-value. I personally prefer Charts Plotly's behavior, but I may be biased because it's what I need...

The problem is that identical x-values (dates) are getting merged together at some level (in Charts?). This results in x and y series of different lengths (observed via the Charts debug output), and not all of the data gets plotted/some data gets plotted incorrectly. For my particular case, this problem gets more pronounced if I use a less granular date representation for the x-values. Here's the same data but using the "HTML month" formatter instead of "HTML datetime":

I'm not doing any aggregation in the View.

Anyway, short version: I think that if Plotly's line plots behave this way (which I like!), then Charts should not be attempting to group the data in a line plot (if that's what's going on).

Steps to reproduce

Create a line plot with a data series that has points with identical x-values. View the Charts debug output to see x- and y-vectors of different lengths.

Proposed resolution

Don't merge duplicate x-values in line plots.

Remaining tasks

User interface changes

API changes

Data model changes