I'm guessing that if the group breaks up, that means they feel really secure and at home in your tank.
also a quick question for you cory lovers! i have 8 cory fry, at what size can i put them back in with the adults? at the moment they are around 3 weeks old and still very small. (a cm or so long?)
26.5 C. is not suitable for most Corys, in spite of a few months experience.