When the robot bumped the system, gas rose through the vent that carries warm water down to prevent ice-like crystals from forming in the cap, Coast Guard Adm. Thad Allen said.
The cap was removed and crews were checking to see if crystals had formed before putting it back on. Allen did not say how long that might take.
"There's more coming up than there had been, but it's not a totally unconstrained discharge," Allen said.
In the meantime, a different system was still burning oil on the surface.
Allen also announced that two people working on the oil-spill response effort died, but the deaths were not work-related. One of the victims was working on a vessel near Gulf Shores, Ala., and the other was a swimming-related accident, Allen said. He did not elaborate.
Before the problem with the containment cap, it had collected about 700,000 gallons of oil in the previous 24 hours. Another 438,000 gallons was burned.
The current worst-case estimate of what's spewing into the Gulf is about 2.5 million gallons a day. Anywhere from 67 million to 127 million gallons have spilled since the April 20 explosion on the Deepwater Horizon rig that killed 11 workers and blew out a well 5,000 feet underwater. BP PLC was leasing the rig from owner Transocean Ltd.
Meanwhile, the Obama administration tried to sort out how to resurrect a six-month moratorium on new deepwater drilling that was struck down by a federal judge a day earlier.
U.S. District Judge Martin Feldman in New Orleans, saying the government simply assumed that because one rig exploded, the others pose an imminent danger, too.
Feldman, a 1983 appointee of President Ronald Reagan, has reported extensive investments in the oil and gas industry, including owning less than $15,000 of Transocean stock, according to financial disclosure reports for 2008, the most recent available. He did not return calls for comment.
The White House promised an immediate appeal of his decision. The Interior Department had imposed the moratorium last month in the wake of the BP disaster, halting approval of any new permits for deepwater projects and suspending drilling on 33 exploratory wells.
Interior Secretary Ken Salazar said in a statement late Tuesday that within the next few days he would issue a new order imposing a moratorium that eliminates any doubt it is needed and appropriate.
"It's important that we don't move forward with new drilling until we know it can be done in a safe way," Salazar told a Senate subcommittee Wednesday.
BP's new point man for the oil spill wouldn't say Wednesday if the company would resume deepwater drilling in the Gulf of Mexico.
Asked about it Wednesday on NBC's "Today" show, BP managing director Bob Dudley said they will "step back" from the issue while they investigate the rig explosion.
Also Wednesday, BP said Dudley has been appointed to head the new Gulf Coast Restoration Organization, which is in charge of cleaning up the oil spill.
At least two major oil companies, Shell and Marathon, said they would wait to see how the appeals play out before resuming drilling.
The lawsuit was filed by Hornbeck Offshore Services of Covington, La. CEO Todd Hornbeck said after the ruling that he is looking forward to getting back to work. "It's the right thing for not only the industry but the country," he said.
More on the Disaster in the Gulf:
BP's Dudley Takes over as Point Man in Gulf
Tough Questions Confront Gulf Spill Claims Czar
White House Seeks New Oil Drilling Ban
Salazar Seeks to Re-impose Drilling Moratorium
Sources: Gov't Report Says Subsea Oil a Problem
Judge Who Tossed Drilling Ban an Oil Investor
Judge Blocks Offshore Drilling Moratorium
BP CEO's Stand-In Heckled at Oil Meeting
Sea Turtles Swimming Into Big Trouble
What Stops Oil Spills on Other Rigs?
Gulf Kids Devastated by Oil Spill