According to "Corals" by Eric Borneman:
"Reproduction by colony budding for both types of plerogyra (genus) is fairly common in captivity" - page 314, see "collection impact", first column.
I have an awesome piece of bubble I got about a year ago, but I have not seen any signs of budding. I am interested to know if anyone has bubble coral reproducing by budding in his/her aquarium.