Unexpected behavior of undeclared parameter in MatrixOP

I have discovered a behavior that I did not immediately expect. Consider the code line below.

I set this up to extract a plane from a stack prior to processing. I inadvertently did not declare cplane as a variable nor assign it a value before this code line. Despite this, oddly enough, the compilation threw no errors and the code runs without errors. What essentially happens is that simgplane becomes the entire image.

I hazard a guess that, without declaration, cplane becomes equivalent to NaN in the MatrixOP call, and the MatrixOP extraction then blissfully extracts all planes.

Perhaps a more robust check on the status of index values used in the MatrixOP source wave is warranted?

Igor Pro 8.x