Mark an mail as read manually

I want to mark a mail as read manually. An icon is missing but there is an right click context menu which offers everything. When I place the cursor on a mails body the context menu opens with a right mouse click. But whe I try to choose  “mark as read” the cursor always moves to categories and eM7 hangs. It is almost impossible to choose something else than “categories”.
This seems to be a severe error and I wonder why nobody has found it. Maybe my eM7-Installation dosn’t work well.

Do you have any solution for this problem?

It works better when I use the context menu behind the little arrow. Marking as read works but whenever I touch categories in this context menu eM7 hangs.