In recent editions of Canon's Digital Photo Professional (beyond version 3.11.10 or later) a lens correction tool known as Digital Lens Optimizer (DLO) has been added. It uses Canon's own knowledge of the complete design and performance of Canon sensors and lenses to apply comprehensive lens correction to RAW files. Applying DLO correction to a .cr2 file doubles the size of the RAW file. If the DLO correction for that file is later unchecked in DPP, the file size reverts back to the original.
What could cause this?