Misleading documentation of setKeyValueAt()

The only description of what setKeyValueAt() does is here: http://doc.qt.nokia.com/4.6/animation-overview.html#animating-qt-properties
It describes what I would expect: I set certain points and the interpolation goes through/by these key values. That is the concept of keys in all animation tools (e.g. Flash, Blender).
See the attached image for how I (and potentially other users) interpret the documentation.

However, #QTBUG-6623 was rejected because apparently the interpolation supposedly does not go through key values. But with my tests, Imho, it goes through/by these key values in Linear easing but not in any other easing.
The documentation of setKeyValueAt() itself does not say anything, the meaning of step is unclear.

Also, there is no is in no example/demo/autotest where setKeyValueAt() is used with step other than 0.0 or 1.0. So, there is no code that I could read to understand what the use case of setKeyValueAt() is.