When I click on Members in the Activity tab on the primary navigation bar, the result is a search page instead of the list of members.

Is this a bug or was this a change that I missed?  If it is a but - how do I fix it?

There is no "Members" on the activity tab by default. I presume you created a custom link to the list of members - in 4.4.5 you probably need to add &tags=X to the URL for the list to show due to a recent bug fix.