There appears to be some disagreement between the two parties on whether the Dem caucus "sanctioned" Lieberman or not, reports the Politico:

“I don't view it as a sanction,” a relaxed and genial Lieberman told Politico as he walked through the Capitol. Instead, the Connecticut independent suggested he relinquished his seat on the committee voluntarily — “in the spirit of cooperation” — after Senate Majority Leader Harry Reid (D-Nev.) asked him to help free up room on the committee for incoming senators....

A Reid spokesman “disagreed” with Lieberman's characterization but declined further comment. One senior Democratic aide, who reviewed the Lieberman resolution that passed 42-13 by secret ballot, also disputed Lieberman's contention, saying it explicitly called on him to “relinquish” the EPW seat.

“It's a sanction,” the aide said. “Someone who serves on a committee for 20 years just doesn't drop it in the spirit of cooperation. It was taken away from him — and that's obviously what happened here.”None of the senators emerging from Tuesday's closed-door meeting shared Lieberman's interpretation. Some were appalled that he had gotten off so easily, but none expressed the opinion that the EPW action wasn't intended to send a message to Lieberman.Vermont Sen. Patrick Leahy, who wanted Lieberman stripped of his Homeland Security post, decried the loss of the panel seat as “a slap on the wrist.”