A simple script that reads a CSV file and writes it to an output file just renames the input file to the output file.
This optimization should not be applied to input files but only to temporary scratch files.
Judging from quick local checks, this bug does not seem to affect data_type='frame' inputs, but only data_type='matrix'. Test script is attached.
Tested on current master git branch (ef8b551103085b73d0b471db9df6c5c0748f7d94) on the file