Ever have this one happen?

[canadaump6]

Batter runner hits a groundball, slides into first base, beats the throw, then his foot comes off the base while his body is facing home plate. 1st baseman has the ball in his glove and foot on the bag. Is this a force out now that the batter runner has come off the bag?

0 out, R1. Ground ball is hit to the second baseman, who throws to 2nd but
R1 beats the throw there. As the shortstop comes off the bag to throw the ball back to the pitcher, the runner starts trotting back to first base. The shortstop steps on the bag with the ball. Is the runner out on the force?