Looking at the image that you supplied, I would say that you have run out of room, there is not enough space to house the last menu item.
The following will help solve the problem
- Increase the available space
- Decrease the space required per menu item
- A combination of 1 and 2
Same poster different browser...hence different "screen-name"
I'm learning slowly
For the width of each menu item you might try a percentage like width: 20%