If you enter an invalid smart card certificate issuer filter in the ThinLinc Client options, it's silently accepted and results in that no filtering is done.
This is printed to tlclient.log when the ThinLinc client starts:
> 2021-11-02T13:40:48: Malformed token "MYINVALIDFILTER"
Nothing is shown to the user. We should be able to warn the user or disable the "OK" button perhaps?
Note that the filter can also be found in tlclient.conf, and that a user might edit that file directly.
This setting is found here:
Options -> Security -> Smart Card -> Details -> Add new/Edit Certificate filter