Attribute value that's a comma delineated list of numbers is converted to a property incorrectly

The attribute value deserializer is incorrectly handling values like this:

```
value = "10, 20, 30"
```

parseFloat(value) == 10 and this is not isNaN so it's converted to a number.

Perhaps we could additionally check if parseFloat(value) == value. That check will pass because '10.2' == 10.2
