groupby().apply(lambda x:x.copy()) raise error.
```
df = pd.DataFrame({"g":[1, 2, 2, 2], "a":[1, 2, 3, 4], "b":[5, 6, 7, 8]})
df.groupby("g").apply(lambda x:x.copy())
```

raise 

```
ValueError: Shape of passed values is (3, 4), indices imply (3, 2)
```

but `lambda x:x` or `lambda x:x[:]` works.
