In the Gradebook, if Preferences>Grader Report>Show column averages is set to "No" the last student entry row in the gradebook becomes sticky.  Basically because the last row is normally the average and is set to be sticky, if this row is hidden, the last student row instead becomes the sticky row. 

To reproduce: Set "Show column averages" in grader report preferences to No

Go to grader report with course that has two or more students enrolled.

Scroll up and down.  Row for student who is last in the list will stick. 

Same as MDL-80270 but in 4.5