Bug search for "hpss upgrade" fails to find bug with two tags: "hpss" and "upgrade"

It appears bug search fails to include tags. I just searched for "hpss upgrade" in bzr: <https://bugs.edge.launchpad.net/bzr/+bugs?field.searchtext=hpss+upgrade&orderby=-importance&search=Search&field.status%3Alist=NEW&field.status%3Alist=INCOMPLETE_WITH_RESPONSE&field.status%3Alist=INCOMPLETE_WITHOUT_RESPONSE&field.status%3Alist=CONFIRMED&field.status%3Alist=TRIAGED&field.status%3Alist=INPROGRESS&field.status%3Alist=FIXCOMMITTED&field.assignee=&field.bug_reporter=&field.omit_dupes=on&field.has_patch=&field.has_no_package=>

And I got 0 results. However, I know there is at least one relevant bug, so I tried searching other ways and eventually found <https://bugs.edge.launchpad.net/bzr/+bug/107173> which is open, and has two tags: "hpss" and "upgrade", which is exactly what I thought I had tried to search for!