Users are currently experiencing their selected/highlighted emails in the view pane not holding that selection when they scroll down or up far enough to be out of the current view. After the Notes client refreshes (either manually or automatic) the new selected or highlighted email will be the upper most email in your current view pane. This issue is experienced in the Inbox view, the Sent view, All Documents, etc...
Example:
I select or highlight an email (not fully opening the email) in my Inbox, I scroll down 50 emails or enough emails to were the previous highlighted email is no longer in view. Once the Notes Client refreshes Notes will automatically select or highlight the email that is at the top of my current view and lose my previous selection. This issue is frustrating for users trying to compare or reference specific emails as they are expecting to have their original selected email still selected when scrolling through their Inbox or other folders. This is due to a Product Limitation of the Notes client (see case number CS0336320).