Unable to filter tests assigned to people when more than 50 users

Hi,

When I try to filter tests on a test plan by assigneee, the system can only find the first 50 users.

Attached screen shows how the bottom of the user lists stops at K and searching for a user with S returns no results.

I am able to re-assign the tickets to anyone in the system so this seems to be limited to the filter option

Many thanks,

Marc