It seems that processing a file with the Invert plugin, in pro tools, the transients get effected, in a way, that inverting the “SAME FILE” against itself, with sample accurate alignment, there are artifacts left over, from the cancellation.

This clip discusses, doing a proper controlled Null test, using the Invert Plugin (Processing both, or all audio files in the test, the “Forward Phase file” Twice, and the Out Of Phase file once. It also explains that using the Stereo Dithered Mixer, in PT HD, is definitely NOT the mixer to record tests through. The default HD Mixer, as well as Pro-Tools LE mixer, are the only Mixers suited for recording “Through”, when recording nulled results.