Inbox - right click on mail item

Hello, I have a few client machines where the user will be in the inbox, and have the ability to right click a mail item to select an action on the mail, ie, delete, forward, etc. However at random times during the day this functionality disappears, and they lose the ability to right click and get that menu. The only way to get it back is to close Notes and reopen. Users are using 8.5 client with 8.5 template. This happens with textured workspace on or off. And of course, it works perfectly till I walk away. Has anyone seen this ? Is it possible they are hitting some sort of mouse click - keyboard combination that would disable the right click / menu on a mail item ?