Weird formatting behavior

this code:
```rust
let x = f16::from_f32(std::f32::consts::PI);
println!("{:.1e}", x);
println!("{:.1e}", f32::from(x));
```
produces this
```
3.140625e0
3.1e0
```

`f16::debug` just uses `fmt(self.to_f32(), f)` so I don't know what might be causing this