bug searches with underscore (_) words don't match anything

Searching for maps_protect in procps should return bug 269715 (which you can find by searching on just protect), but it doesn't return anything.

my search URL is
https://bugs.launchpad.net/ubuntu/+source/procps?field.searchtext=maps_protect&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=

if there's some help somewhere on special characters in search, it wasn't obvious enough for me to find it, even though I had a quick look on the advanced search page.

 Anyway, _ can be part of tokens in most programming languages, which is actually maybe a good argument for the bug search treating it as a word character.