PUBLISHER tag in Index Tags trouble

[Stake]

Trying to reproduce the problem I ran into a very odd situation.

Using foobar2000 I added a "Publisher" tag to a few files and populated it with "Sony". The result was reflected correctly in MP3Tag.

I added "Publisher" to the index tags, saved, restarted and recanned the server.
Oddly enough there was no sign of Publisher in the list view, neither on the WiiM Home app, nor on mconnect.

Then I repeated the exercise with a wildly made up tag called "Trala" and again pupolated it with "Sony". This will show up in the both apps as a selection criterion.

Is there some sort of ban on "Publisher"?