Sorry, I should have been more specific...the disconnection has to be from the mother's side, since she still showed the separate connections to the "two" merged sons.
Profiles are never deleted. Even after merging, the original profile still exists. But its not supposed to be visible and original one will always redirect to the final one.
But sometimes, depending on the order of events, the old data gets "stuck" in the database base fields, and is not cleared out properly. If we knew the exact steps to reproduce this problem, the code could probably be fixed. Meanwhile, the workaround is to simply disconnect and reconnect.