A “discrete” axis mapping yields unexpected and non-ideal `fvar` instance records

I’m currently using FontMake 3.6.0 (the current release).

I have a designspace which seems to _mostly_ be building well with:
- An `ital` axis with a mapping to make it a discrete, binary, on/off axis
- A single variable font, including the full ital range

My goal is to have an `ital ` mapping which makes the axis work like an on/off switch. As far as the variable axis input (e.g. a “slider” interaction), this works as expected:

```xml










```

_However,_ I’ve noticed that this axis map yields unexpected instance and axis-value matching. Specifically, instances that should be assigned `ital=0` actually get assigned `ital=0.49994` in `fvar`. And then, these instances work incorrectly in apps like [WakamaiFondue](https://wakamaifondue.com/beta/) and [Fontdue](http://fontdue.com). I’m just guessing, but these apps probably look up the instances in `fvar`, then round this to `0.5`, and that value is mapped to `ital=1`. So then, the result is duplicate instances, all pointing to italics.

Here’s a snippet from `fvar`, showing what I believe to be the problem:

```xml







```

This is unexpected, because my designspace has that instance set up like this:

```xml









```

I would expect my Italic `xvalue="0"` to make it into `fvar`, but ... I guess I can also see how it matches two `output` spots in the axis map, and it can’t really know which `input` value to match, so it defaults to the higher of the two possibilities.

Still, this isn’t ideal. Is there a way to have a discrete axis map, and avoid this unintended `fvar` result?

I have found a workaround, but it doesn’t feel ideal...

To get the upright instances to be assigned `ital=0` as desired, I have to do what feels a little hack-y in the map, adding other small values to the axis map:

```xml










```

That way, the instance definitions only match a single output/input exactly, and this yields an `fvar` table with instances that look better:

```xml







```

And this variable font seems to work better in WakamaiFondue.

Is there a better way than making sure to include small values in the `map` element? Should there be?