Found a mistake in the docs:

http://tensorflow.org/get_started/basic_usage.md

In the "Variables" example, looks like a variable name got changed but not updated everywhere:

    # at the start:
    var = tf.Variable(0, name="counter")

    # then:
    one = tf.constant(1)
    new_value = tf.add(state, one)
    update = tf.assign(state, new_value)    
    

The variable "state" should be the variable "var", or vice-versa.