So is there now more than one rosette that looks different from the original plant? Could you show a picture?
Re. conditions - It normally works the other way... growing in drier, sunnier conditions usually causes the plant to produce smaller, more compact growth, not larger and looser growth.
What I notice is that the large rosette(s) has a different leaf shape - oblanceolate, as compared to rhombic on the main plant.
With respect to the odd rosette(s) being "mature" while the others aren't, if you look at your picture above with the plant in the dealer's pot, that's a mature rosette that the offsets are growing from, and it has rhombic leaves, not long, loose oblanceolate ones.
I could be wrong but I still suspect a Draba seeded itself in your Androsace clump.
If you have more current photos, showing both sorts of rosettes, there are other places you could post them for an expert opinion, e.g. Scottish Rock Garden Club plant ID forum:
http://www.srgc.net/forum/inde...
