Album Artist is handled properly, I don’t have a problem there with multi-text values.
However any other custom tag is not OK.
If the multi-text property is only applied to newly updated values, I have tried adding a new multi-text TAG, not present in any file.
First I have defined TEST_GROUPING as multi text:
Then I have created a new Tree Query based on TEST_GROUPING:
After that I have restarted TuneBrowser, just to be sure, and I have imported a new test album including TEST_GROUPING for the first time in my library:
However the result was still not as expected even if these were brand new files, not stored before the change:
If there is anything else I could try, please let me know, I would gladly help in any way if I can.