Similar experience with my GBTA. It split a month or so ago, then the clone split as well and I now have three. The second split did not happen right away, but I kind of suspected it would since the clone stayed quite stretched out for a week or so until it finally split as well. All looking good at the moment and they've stayed very close together, my Maroon Clownfish pair are in anemone heaven.
I think I may have the GBTA from hell anyway. It's been through some times of ill health and moved under the rockwork out of the light once on me as well. I had to re-aquascape to get it back into the light and healthy. It was getting quite bleached after a month in the unsuitable location. No idea why it did that or didn't move back into the light on its own. Prior to the recent split, it also went through a 'non-split' event on me about a year ago. Check out the link below.
I'll have a couple of GBTAs for sale soon as well, if I can figure out a good way to get the clones to detach. They're anchored pretty well and I'm sure my Maroon female will not take kindly to me poking around there trying to disodge them. If the mother nem is any indication, the clones will be quite bullet proof if I go by what it's been through in the past 3 years.
http://www.canreef.com/vbulletin/showthread.php?t=54984