To reproduce:  
- Switch to tab-mode(Z) and select the article tab  
  (Btw the menu entry doesn't change to "View Tabs as Panes", as it once did(?))  
- Select an article  
- After download switch back to the article tab  
  
Now nearly every action on the tab forces a switch to the message tab, including  
- expanding a thread  
- clicking on the column headers to resort  
- even a right click on the selected article header  
 
Similar, if selecting a new group on the group tab, you can observe a double switch 
first to the article tab, and shortly afterwards to the message tab. Quite funny. 
  
This renders the whole tab mode almost unusable.  
  
Sincerely  
Roman