iTunes tags not removable (reappear after being deleted)

I used iTunes to convert some files from .wav to .aiff and while doing so it created two tags:
"comment [iTunNORM]" and "comment [iTunPGAP]". The IDs are comment:iTunNORM and comment:iTunPGAP, respectively.
However, everytime I try to remove these tags they reappear after reloading the affected tracks into picard.

I've done it the usual way: selecting the track -> selecting tags to be removed -> removing tags -> saving the track

After removing the track from picard and loading it again the previously deleted iTunes tags appear again.

I am, however, able to edit these tags, i.e. changing the value and save it successfully/permanently.

Someone [outsidecontext] told me that "There is actually some code in place to prevent the deletion of those special iTunes tags."

How to deal with this, i.e. remove these tags?

note: I'm pretty new here so feel free to make any changes to this post.