I think you can disable "allow multiple", this is currently bugged though so I´m not certain. (Should be fixed next release)
Other than that, it makes sense for the sprite to move like this. While both tweens run the first two seconds, the sprite moves ~283 pixels per second. Then one of them is done tweening, now only the 3 second long tween is still running at ~33 pixels per second. Considering you move ~566 pixels in the first two seconds, it finishes the remaining 34 pixels in 1 second.
EDIT: Speaking of the next release... it did just release that second :D