In the famous Up Is Down scene in Pirates of the Caribbean: At World's End, they manage to make the Black Pearl capsize and turn 180 degrees by merely running back and forth between port and starboard. Plus letting loose the cargo below deck, which feels like a quite dangerous decision given the damage done to the support beams of the ship by the canons, as shown in the scene itself.
However, later in the movie, having many of the crew run or stand on one side of the ship doesn't seem to make the ship move much, if at all.
When Jack escapes the Endeavor by pulling his mad stunt, we see many people run to one side of the Black Pearl and the ship doesn't seem to move even an inch.
Later on, during the battle at the maelstrom, a lot of the crew are gathered on one side, preparing to board or fire on the Flying Dutchman, the ship is listing to the same side thanks to being inside the maelstrom, yet it doesn't capsize. And the many people balancing themselves on ropes to actually board the Dutchman doesn't seem to have any effect on the already listing ship as well.
So, how comes the Black Pearl was easily made to capsize and do a 180 degrees turn in the locker, but was able to stay afloat in much harsher conditions in the maelstrom?