ReflectionClass::getProperty returns incorrect class attribute

See https://3v4l.org/v0vtF for output of the test cases for a number of php and hhvm versions.
### HHVM Version

Initially seen in 3.6.6, also confirmed with 3.12.0
### Standalone code, or other way to reproduce the problem

``` php
getProperty('test');

var_dump($property);
```
### Expected result

```
object(ReflectionProperty)#3 (2) {
["name"]=> string(4) "test"
["class"]=> string(1) "a"
}
```
### Actual result

```
object(ReflectionProperty)#4 (4) {
["info"]=> array(10) {
["name"]=> string(4) "test"
["default"]=> bool(true)
["defaultValue"]=> NULL
["access"]=> string(9) "protected"
["accessible"]=> bool(false)
["modifiers"]=> int(513)
["static"]=> bool(true)
["class"]=> string(1) "a"
["doc"]=> bool(false)
["type"]=> bool(false)
}
["name"]=> string(4) "test"
["class"]=> string(1) "b" // should be "a"
["forceAccessible":"ReflectionProperty":private]=> bool(false)
}
```