Client hours do not change on updating the actual hours if the Client Hours column is visible in the Time Entries list view.
When both the Hours as well as Client Hours columns are visible, they behave as independent fields. So you have to update the hours manually in one of them. When one of the columns is hidden, then they are dependent and the changes reflect on the other automatically. So when you update the actual hours, client hours are also updated automatically, provided actual hours value is not less than the activity or fee schedule minimum hours (if applicable).