yapf disable setting is ignored & breaks formatting

using the 0.29.0 release

this code snippet:
```python
def str_ms_flags(flags):
return decode.str_bits(flags, {
MS_ACTIVE: 'active',
MS_NOUSER: 'nouser',
})
```

when using `# yapf: disable`, it reformats incorrectly as:

```python
# yapf: disable
def str_ms_flags(flags):
return decode.str_bits(flags, {
MS_ACTIVE: 'active',
MS_NOUSER: 'nouser',
})
```

using the default style settings here.