I slept through the stage today, and won't pass judgment based on a 30 second video. Earlier in the race (Stag 2?), Contador was in a group with Armstrong and others with other dangerous riders ahead, but Contador heard that Schleck had a problem behind, and insisted against some argument that the group wait.
On Stage 2, Cancellara declared the stage neutral. On Stage 3, on the pave, Cancellara led Schleck on a mad chase to put time into Alberto and others. Someone ran into Contador's rear wheel and broke a spoke. The rear brake rubbed, and it got increasingly worse over the thirty kilometers. He couldn't stand up to pedal, and he ended up losing time on his own chase group at the end. He said afterward that he couldn't stop to change the wheel or he would have lost even more time.
Schleck gained a minute and thirteen seconds on Contador that day. It's the reason he has been in the yellow jersey at all, after finishing 42 seconds behind Contador in the Prologue. I don't know about shifting on a climb, and if a Schleck mistake caused the dropped chain. But keep his behavior on Stage 3 in mind before you pass judgment on this one.