M4A not recognised as stem file in Traktor

Hello,

I’m experiencing an issue when editing Traktor Pro 4 stem files with MP3Tag.

Situation:

I generate stems using NUO-Stems.

The files are correctly recognized as Stem files in Traktor.

To test this:

I create a stem file.

I make a copy of the file.

Both files are recognized as stems in Traktor.

I run an MP3Tag Action Group on the copied file.

After saving, Traktor no longer recognizes the file as a stem file (it loads as a normal track).

Notes

Some basic edits do not break stem recognition, for example:

changing the TITLE

editing COMMENT or ALBUM

However, when running my full Action Group, the file loses stem recognition.

The action group mostly does:

tag formatting (YEAR, TRACK, LABEL, GENRE)

many Replace "_ALL" cleanup rules

Camelot key conversion

Case conversion "_ALL": Mixed Case

clearing some tags

renaming the file %ARTIST% - %TITLE%

Question

Is it possible that one of these actions causes MP3Tag to rewrite or remove non-standard metadata chunks in the file container?

Traktor stem files contain extra internal metadata that identifies them as stems, so I suspect something may be modifying that.

Can someone check what is being edited so i can remove/change that?

Files can be found here: Stems_check – Google Drive

Can you try with the option Settings → Advanced → Reuse unmodified MP4 atoms enabled?