Scenario:
On entering time on the timesheet by selecting a client and then entering time against a project and saving it, the Client name selection reverts back to All.

Reason:
The only time you can reproduce this issue is when the Application is set to Not use billing information, which means that in the System Preferences page in the Usage page, the Use billing information is unchecked. The Client selection is not saved only for Single client method projects. Projects which have multiple clients allocated retain the client selection made.