MP3tag seems to remove the trailing space from the iTUNNORM tag, making iTunes think it needs to re computed.
I believe the bug is located in actions that use the _TAG tag, to adjust all the tags at once instead of individually. do you think you guys could exempt iTUNNORM from the "_TAG" selector?
tl;dr if you remove trailing spaces, and the _TAG selector to select all tags, it will corrupt iTunes's Sound Check data, which is stored in the ITUNNORM tag. In order to solve this issue, you should exempt iTUNNORM from the _TAG selector. there are literally no downsides to this, as the iTUNNORM tag contains binary data and should never be subject to data manipulation in the first place.