Thanks for checking and confirming the issue. Yes it seems like a bug to me too.
The reason this is more than a “useless warning” is due to the circumstances of when it occurs. The nature of the Surface Viewer and other similar utility objects is to parse entire lists of available attributes. A separate warning is generated by each missing index number, both when you regen the 3D window and when making any changes in the settings dialog. And each warning requires a key press or mouse click to dismiss. So even if I’ve been diligent in keeping our template tidy, if an attribute creeps in with a large index number I might be looking at a hundred or more key presses to get the script to run. So these objects are essentially useless until this bug is fixed.