HPCC-11984 Group Members List Corruption

When selecting users for a Group, items sometimes disappear.

Fixes HPCC-11984

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #6400 from GordonSmith/HPCC-11984

HPCC-11984 Group Members List Corruption

Reviewed-By: Miguel Vazquez <miguel.vazquez@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>