problems with Artist.displayFormat

[Alhifi]

Hi experts,

after updating from 0.8x to 2.1 I have problems with the "Artist.displayFormat" which is used at "tagformat". I organize my music as followed:

example:
artist=Artistname
composer=Feat. another artistname

I still use Roku Soundbridges and want to show the complete artist+composer while playing a title, therefor I have defined an displayFormat for Artist, which looks like the following:

Artist.displayFormat={$artist$composer^_}

(I also tried Artist.displayFormat={$artist$composer^^^_} )

Normally the result should be

Artistname_Feat. another artistname

(where the _ is here a symbol for the space I configured normally as prefix or in the other version as separator)

If the file did not have a composer tag, the artist ist displayed, which might be correct, if the file has an artist and a composer tag, only the composer is shown and not the combination.

Simple question: Why?

kind regards
Alhifi