When left clicking on the seek slider the calculated position is incorrect. The same happens when grabbing the slider's handle, dragging and dropping it.

The reason is that in SeekSlider.OnButtonReleaseEvent() when translating the clicked X coordinate into the seek value, instead of the slider's actual seeking width it takes the control's width which is slightly bigger as illustrated below:

<- width of the control ->
[-]----------------------
 ----------------------[-]
 <-    seeking width   ->

I'm not sure if it's possible to get the actual seeking width from HScale, however the middle mouse click works just fine. May be the left click should be translated to middle click (see also bug 565795 which originally requested this feature.)

Steps to reproduce:

 1. Start playing a song, longer songs will result in bigger seeking mistakes. I will use a 5:00 song as an example
 2. Grab the seek slider handle with left mouse button and drag it to about 30 second mark.
 3. The playback jumps to about 50-55 seconds.
 4. Try again, this time to the 4:30 mark.
 5. The playback jumps approximately to 4:05.
 6. Now instead of dragging the handle just click on the slider. 
 7. Notice how the handle lands to the right of the mouse cursor when you click near the beginning of the song, to the left when you click near its end, and under the cursor when you click in the middle of the song.