Having trouble with Lock Screen controls

[ThousandEyes]

I've got a Samsung Galaxy S5 with a premium account and while I can use the lock screen to change songs I can't use the lock screen to select specific points in the music.

When I try and do so the timer just sits at the selected time unless I close the screen and re-open it, at that point it moves back to the current time and, if playing, continues on its way.

Not sure if I'm doing something incorrectly or if it's just not possible to select a specific point in the song through the lock screen. It seems like the addition of the timer for songs on the screen would indicate that I can.