Setting player position Can Fail
Setting the player position while the iTunes player state is paused resets the player state to stopped and resets the player position to 0.
tell application "iTunes"
play -- initialize the state to Play
pause -- put iTunes in Pause mode
set player position to 5
log (get player state) -- will be stopped
log (get player position) -- will be 0
end tell
Attempting a workaround, I found that as long as the track isn't paused, the player position can be set.
This did not occur in previous versions; setting the player position while paused would, as expected, move the play head to that position. In fact, Needle Drop uses a variation of this to begin playing a track at a user-set start time. Needless to say, this won't work with iTunes 12.4. (Hat-tip to Correspondent Rob Robinson.)
[UPDATE: Needle Drop v5.3 addresses this issue.]
[UPDATE ALSO: this issue is fixed in iTunes 12.4.1.]