Teachers are human. It's human nature to want to discuss what is bothering you with other teachers. However, it's unprofessional to just complain and gossip about other students. I'll admit that sometimes I'll discuss problem students with colleagues, but generally it's more to get ideas on how to deal with it, and unless the teacher I'm discussing it with has something to do with that child's education (music teacher, computer teacher, etc.), I don't name names.