I guess I see it as tactlessness and insensitivity, which worries me in the context of therapy, because of course we all want a sensitive and empathic therapist. If I'm seeing a regular GP weekly and s/he is going away on a vacation, I would think that s/he would inform me about any changes in schedule the week s/he returns beforehand. It's a professionally sloppy thing to not do, I think. But with therapy, it brings up a lot of feelings.