I think I have found a small bug.
As the title says, it is currently impossible to delete a tag field from a WavPack-encoded DSD file. It is however still possible to add a new tag field. When having deleted that tag field again in the small tagging window, and then clicking apply, the value immediately reappears. Rather annoying when you accidentally entered something in the wrong field. I need to use wvtag.exe to delete the field and then use 'reload info from file(s)' from the context menu to work around this.
Interestingly, deleting a tag field from regular PCM WavPack files works normally.
Using foobar 1.4.2 on Windows 1809
File is not playing while editing tags
I can happily provide a test file or any further details if necessary.
You use foo_input_sacd to handle WavPack-DSD? If so, this is foo_input_sacd's bug. You can try to report it on https://sourceforge.net/p/sacddecoder/bugs/ Native fb2k's wavpack reader can properly edit/delete tags in wavpack-dsd (yes, fb2k natively supports playback of wvapack-dsd (since version 1.3.13)).
Ah yes, that's it. When I remove foo_input_sacd, the tagging works again as expected.
I did not expect that that plugin would have anything to do with tagging.
Thanks for your help!