Using discnum or tracknum as a filter in tagnavi submenu

[anonamoth]

This does not appear to work properly. All available disc numbers or track numbers are listed, however, once selected, ALL titles are displayed and no titles are filtered out.
ex.
"Audiobooks" -> artist ? grouping ~ "audiobook" -> album -> discnum -> title = "fmt_audiobook"

After selecting an album, a list of available discs is displayed:
<All Tracks>
<Random>
1
2
3
4

Whichever disc number is selected, all titles from all discs are displayed, rather than only displaying the titles from the selected disc.
The same issue occurs when using tracknum as a filter.

It seems fairly significant that a filter simply doesn't work at all. In the Database Wiki chart, it lists both tracknum and discnum as filter options. Does anyone have experience with this or have it working for them? Could it be a bug? I checked the flyspray database bug entries and nothing was listed.