How to find source of TF_NAN_INPUT error

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While using amcl and move_base I'm getting the following errors while applying a tf_prefix. It worked without the prefix but now that I'm using it, I get the following error:

remote[red1-0]: Error:   TF_NAN_INPUT: Ignoring transform for child_frame_id "robot_tf/odom" from authority "unknown_publisher" because of a nan value in the transform (nan nan nan) (nan nan nan nan)
         at line 240 in /tmp/binarydeb/ros-indigo-tf2-0.5.15/src/buffer_core.cpp
Error:   TF_DENORMALIZED_QUATERNION: Ignoring transform for child_frame_id "robot_tf/odom" from authority "unknown_publisher" because of an invalid quaternion in the transform (nan nan nan nan)
         at line 253 in /tmp/binarydeb/ros-indigo-tf2-0.5.15/src/buffer_core.cpp

From the error listed above, what transform is being ignored? To the robot_tf/odom frame? What is the authority (I know that it says "unknown_publisher" but what is an authority in this context)?

At this point, I'm just trying to figure out how to read this error so that I can figure out where the issue lies. I know that TF_NAN_INPUT means that somewhere NaN values are being set in a transform and TF_DENORMALIZED_QUATERNION means that somewhere a denormalized quaternion is being set.

In case it is useful, here is the error that roswtf reports:

ERROR TF multiple authority contention:
 * node [/robot/laser_broadcaster_NGNeuromorphic1_18892_5059838883645381072] publishing transform [robot_tf/base_laser] with parent [robot_tf/base_link] already published by node [/robot/robot_tf/pioneer_transform_node_NGNeuromorphic1_18892_3963024023289368467]
 * node [/robot/robot_tf/pioneer_transform_node_NGNeuromorphic1_18892_3963024023289368467] publishing transform [robot_tf/base_laser] with parent [robot_tf/base_link] already published by node [/robot/laser_broadcaster_NGNeuromorphic1_18892_5059838883645381072]

and the output from rqt_tf_tree: