Advanced Search : Ability to search on custom activity fields which extend a specific activity type is missing

In 3.0.4 - users are able to search on custom activity fields in Advanced Search -> Activities pane, regardless of whether these custom fields extend ALL activities or a specific activity type. In 3.1.3 - this ability seems to have been broken / removed unintentionally. You can still search on custom activity fields that extend ALL, but custom fields which extend an activity type (even though they are marked 'Searchable') do NOT appear on the advanced search activities pane form.

This is a regression bug and s/b fixed as soon as possible. I've assigned to 3.1.4. However, if this is a trivial and safe patch - would be great to have in 3.1.3.