Hit ENTER after each Tag to add it to your post; Numbers in parentheses represent the Tag's usage.
I reproduced this problem with SmarterMail 13.3.5535 Free and Enterprise.
1. Open your Inbox in the browser (IE11 or Chrome)
2. Click the arrow on the Content Pane to hide the Folders Pane
3. Resize the pane that lists your messages
4. Click the arrow to show folders pane (it doesn't work)