I really appreciate your help, thanks!

Don't feel bad. It took me a while to figure this out.

If you define a multistate data point in a virtual data source, you need to define values for the states. On the Virtual data point dialog shown above, when you mouse over the area under Values, up and down arrows will appear at the right side of that field. You can use those arrows to adjust to your first value, or just enter a number directly.

Once the correct number shows for your first value, hit enter. Your first value will now appear on a white background, like this:

You will note that the dialog is now helpfully suggesting 2 as the next value. If that works for you, just hit enter, and you will see this:

Repeat this process until you have defined all your values for the multistate data point.

Now when you click in the Start value field, you should see a list of the values you just defined appear over the field. Select the desired value.

The above is what is working for me. However, there is a known bug with this dialog.

Once you define your multistate data point and save it, if the change type is "no change", when you try to edit it you will not see the state values or the start value you defined. The dialog will not let you save changes until you again enter state values and a start value. This again is a known bug that I expect will be fixed in a future release.

Could you export the JSON for the point and share it?

Since you showed me how to define values for a multistate data point, I no longer have one without a start value.

You should be able to drag and drop them on the forum's reply window, but that would upload them to imgur. So, if that's a concern, don't upload the screenshot.

Hmmm.... didn't work the first time I tried it.

It may not be so intuitive, but you can define states which will appear in the drop down by hitting the enter button when typing in the "Values" field in the new UI. Using the latest released Mango, I was able to change a virtual binary point to multistate and back.

Indeed. Not very intuitive. But it does indeed work as you explain.

Can you share a screenshot? If I open an existing multistate point the save button is not disabled, and I don't need to change anything to be able to save it.

In the situation I describe, the save button is not disabled. Clicking it results in a "Please fix errors on form before saving". Hard to give you a screenshot, as the message clears itself in a few seconds.

Edit: To reproduce this, you would have to attempt to edit a multistate data point that has no start value defined.

Second Edit: How do I add screenshots without making them available on a webserver?

It may not be so intuitive, but you can define states which will appear in the drop down by hitting the enter button when typing in the "Values" field in the new UI. Using the latest released Mango, I was able to change a virtual binary point to multistate and back.

Edit: It seems that this problem also renders already existing multistate data points as uneditable, as in this case, setting a start value is required and the same behavior prevents setting one.

Can you share a screenshot? If I open an existing multistate point the save button is not disabled, and I don't need to change anything to be able to save it.

No contextual field found for key textRenderer.textRenderer.multistateValues

I saw this as well, but it's unlikely to be fixed as it works in the new UI. It is attempting to complain about text renderer validation, but it looks like there's an extra textRenderer. in identifying where the issue is. If the text renderer were valid, I would expect it to be able to save. In the case of that message, it probably meant that no states were defined in the multistate text renderer.