Depthimage_to_laserscan scan height too large (at 1 pixel)

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Im having an issue using Depthimage_to_laserscan. After I subscribe to the topic (uses lazy subscription), it throws an error:

Could not convert depth image to laserscan: scan_height ( 1 pixels) is too large for the image height.

This seems strange to me. Checking the headers of both the image topic and camera_info using rostopic echo, I find they are identically 640x40 pixels (not a typo), the expected size.

Any ideas what could be causing this?

It should be noted that I am running this off a raspberry pi, so I'm using some librekinect and opencv to create the images, with a camera_info_manager to hand out the camera_info. Only the interface to depthimage_to_laserscan causes issues: other uses of the image work fine. This post outlines a possible solution, but does not apply here as Im not using openni.

Thanks