The Constituent search list can be modified in Administration > Application > Features to add additional output fields and filter fields, including a Constituency filter. However, when a Constituency filter is added, and users attempt to filter by the Member constituency, constituents with a lifetime membership do not appear in the results. This occurs even though all of those members have the Member constituency on their records.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.