See https://github.com/zendframework/zf2/pull/5259#discussion_r6932410 and [The PHP Manual](http://php.net/manual/en/language.types.array.php)

> Floats are also cast to integers, which means that the fractional part will be truncated. E.g. the key 8.7 will actually be stored under 8.

`is_float(...)` will never be `true` in this scenario.